Maybe there is more to the mother issue than what we have been told, I wouldn't put it past the show.

Some people commented on it, but Touka's behaviour is pretty odd. If she wants Rikka to "confront reality" that much, why was she trying to stop her from visiting their old home? It seems like a quick and effective way to make her face reality, yet she was doing everything to prevent it, but seemed to go along with it once it happened.

It's certainly true that Rikka and Shinka seem to be avoiding each other.

In my opinion the reasons are as follow:

In the case of Shinka, she doesn't want to meddle with a chuunibyou, it's very hard to talk to Rikka without feeling you're being pulled inside her world. Yuuta himself in the beginning wanted to avoid her, Shinka is probably the same.
Sanae is different because, well she simply cannot pretend she doesn't exist. Shinka actually tries her best to not get herself involved when there's people around.

As for Rikka, it's not just Shinka. In episode 6 we learn that Rikka has problems socializing with any classmates that isn't Yuuta. She isn't ignoring Shinka anymore than she is ignoring Kumin and Isshiki. Whenever the others are talking as a group she tends to isolate herself.
I think this is also why Touka keeps asking Yuuta to help her, she noticed that he's one of the few persons that can communicate with her sister.

I'm counting on it. What it is, though, I don't know: can't take it emotionally after husband dies? Father-in-law pays her to stay away? She's actually dead, too.
She tried to keep Rikka away from this spot, so as not to hurt her emotionally. Once there, however, she tries to use it to wake her up. I'm not saying that's a good approach, but at least there is some logic to it.

I understand where you're coming from. I'm no parent nor even had a girldfriend, but I believe most parents will behave the same way you described, since usually they are more attached to the children than their spouse. Moreover,
It's really unthinkable that their mother would chose to abandon the kids. However I'm in the camp that found Tomoka's decision believable because I think the reverse, while rare, could be the case also (i.e. The husband/wife is more attached to his/her spouse than the children).

It could also be Usagi Drop's situation where
So I think I could accept that part of the story as it is, albeit barely. Of course, a more flashed out and hopefully better than I speculated would be very welcome. Still, I think what really need to be explained is why Touka went through all that to prevent Rikka going to the old house. I mean, she has been away from the town for two years while Rikka was there. It's unthinkable that Rikka never attempted to go to the house in that period of time. Or her grandparent forbided her to do so?
I think that make sense for why she changed her stand right there, but it still doesn't explain why she didn't want Rikka to go to the old house but pushing her to go to the grave. I personally think it hurt equally.

I believe there is a certain difference: going to the grave means she would have accepted her father's death already.
It isn't like Touka is dragging Rikka to visit the grave, but reminding her about that matter surely is a way to make sure she doesn't forget, but that doesn't mean she will accept it. Should Rikka visit their father's grave though, it would be a major step forward and done on her own.

On the contrary, letting her visiting the old house would have the opposite effect: as shown in this episode, Rikka still thinks (or tries to believe?) that her father is alive, and by extention, their house is still there.
Confronting the harsh reality while not ready to accept it would just lead to another conflict and denial, which can potentially scar her even more.

The former requires Rikka to have accepted what happened already, the latter would just be even more painful since she didn't accept that.

I think this is the most plausible way to deal with this issue, and it isn't unreasonable, BUT us having to talk about these issues so much shows some writing issues with regards to the serious part of the storyline. I think the series has done a good job of balancing the comedic with the serious, and is just flat-out fun, but we're starting to find some head-scratching plot issues. In the end, it isn't a big deal, but while I know Chuunibyou is *very* different from Hyouka, I do wish that for its serious plot-line, the writers would have taken the same care as was taken with Hyouka for working out the story details.

I think it's a good reason for encouraging her to go to the grave and not the house, but it's not a good reason for outright preventing it. If the reason for preventing, and not just discouraging, Rikka to go to the old house is it could hurt her, I think it is equally applied to the grave. To be clear, I think it's not a good reason for what Touka did either way.

Touka probably has her fair share of issues, it'd be unrealistic if the whole family tragedy didn't affect her at all.

But if this is not explored in the show, it will be a fault of the scriptwriter.
Only thing that's left is wait and see.

It could be that her busy workshedule kept her from being too visibly affected by it or something like trying to shut down/overwrite that feeling with working hard.
And, while not very effective by now, maybe she think that her being the elder sister, she must serve as an "ideal"-symbol/example.

Painful seeing Rikka in this ep...

A very good episode in terms of psychology. The whole series makes sense because of this episode. But it lays a very heavy burden on the next episode. It could easily break the series, or else leave it unresolved. In a way, I had expected this all to happen in the second-to last episode, in which the outcome of the confrontation would resolve the story. (Specifically, by Dark Flame Master taking her side during the confrontation with the Priestess, this time fighting seriously, and Rikka would realize that overcoming the Priestess would not change reality and bring her father back. The world is not so easily banished.) But given the number of episodes left, I expect non-resolution.

It is quite likely that Rikka's mother suffered a psychotic breakdown and may be unfit for parental duty. Either officially or in her own mind. She may fear that she would do something awful, for instance. Things like that happen. For all we know she may have been mentally frail before - Rikka's happy memories seem to be of her father mainly.

My respect for Touka has been steadily growing. I hope the next episode does not let her down.

I don't see how its not plausible. If you can see the mother staying to remember her husband, I find the opposite happening to have as much credibility.

That is, staying with the children reminds the mother too much of her deceased husband, just seeing her children is just a 24/7 reminder that her husband is gone, and she just couldn't deal with the depression/emotional breakdown and ran away.

Most likely, I mean there hasn't been an episode focusing on it yet, but I think it can be seen. She suddenly has to take on the role of a mother and guardian for Rikka and throw away her golden youth years to take care of her. She has her own emotional baggage with the whole messy family situation, but resolved not to show it in front of Rikka.

My wild theory is that Touka is actually the hero of the story. When she happened to have a recording of Dark Flame Master, it seemed like just a contrived plot device to force him to obey her, and make her seem more evil. But when Touka made her recording, Rikka had already entered her chuunibyou; perhaps Touka waited for Yuuta to grow out of his, then arranged for Rikka to meet him, as someone who could understand her.

She has been kind of pushing Rikka and Yuuta together with her fake hostility. Notice that she treats him harshly when Rikka can see her, but is completely different when Rikka is not around. When Yuuta had spent the whole evening helping Rikka with her homework and then put her to bed, Touka said wistfully that she wished she was the one who could do that. And when she asked him to come with them for the summer holiday, she told him that they needed him. I think this whole episode is part of her master plan. But that is just wild speculation, of course. I have not seen any source material at all, only the anime.

Beautiful episode. Reminds me of Bakemonogatari when they helped Mayoi find her mother's house.

And is Kumin-sempai getting even CUTER?

For me, the mother staying to keep her memories of her husband alive is a subsidiary argument. Normal mothers just don't abandon their children; there are bad mothers, as there are bad people, but there's no sense from Rikka's memories that her mother is out of the ordinary, or especially negligent. The family seems close and happy, in fact, and that can't be sustained by only one good parent. As a friend of mine once put it who's farther into middle age--mothers are amazing things. We're talking about some of the most fundamental connections between human beings--the writers need to give a better explanation of why such bonds just seem to vanish.

Maybe Rikka's the one who accidentally killed her father, and the reason Touka doesn't want her to go back to the house is because it might re-trigger her memories. That's why the house is gone, it burned down and they cleared the land; and that's why the mother abandoned her, because a part of her blames Rikka for the accident and she can't get over it.

This is beginning to sound like Alice in Wonderland...

Natch.

You got all that from 0.5 seconds worth of flashbacks? Honestly, we know next to nothing about Rikka's mother, or what the family situation was like at the time of her father's death. Maybe there's a reason why Rikka is so disturbed by the loss of her father but has yet to show any signs of missing her mother?

Just managed to catch this episode. The subs say Rikka's grandfather don't acknowledge her. Why? Is she not his granddaughter?