If I had to say, talking about the "love triangle", to me this episode pointed out how Chihaya's main point is to restore the "status quo". Looking back at Sumire's question and Chihaya's reaction, the first person she thought was Shinobu and only then Arata. And the last image Chihaya saw in her mind was the tree of them as children back then. So I think that what's she really wishes for is Arata's return to restore that trio. That would explain even her disinterest in Taichi. Taichi is already there so there's no need to worry about him, one piece of her wish is already in the right place. It a sort of behavior similar to her mother, that cared more for the elder sister because more worrisome. And so she is, she is more "worried" about Arata because he is out of her sight. Taichi is doing quite fine and is following perfectly the path she had in her Karuta-mind. (More or less. He is still a B-class, in fact she stated how her priority was him progressing to A-class and everyone got surprised
).
I don't know why she want it. A guess could be that it is like a way to deny the fact that they are growing as much as their impulses. Sosubconsciously she is denying that, trying to stay attached to a childhood's memory. She wants to go back at that stage of life, because it was easier, without any complicated feelings to deal with. A subdue way to tell us that she is not ready for it, for that kind of feelings. That would even explain why she seems so dense. She is dense, but on a deeper level she is simply avoiding to see what everyone else apparently can see (Taichi's feelings for example).
What I think is that basically Chihaya has no real feelings for anyone at the moment.
On the other hand I cant' deny that hints were thrown to imply some sort of interest of Chihaya toward Arata. But as already said they are so mixed up with her idolization, but even idealization, of Arata that is hard to say anything. I think that the idealization of him is another thing that is in the way. We saw Arata so few times that is hard to say anything about him, but I remember a phrase of him that felt out of character (the character I think he is), when he said something about how was useless to keep in touch with his friends in Tokyo, because no way that they would have forgotten about him. Or something like that. If I remember correctly. And even this time he answered in a different way that Chihaya would have expected. So despite the fact that she see him as a god of karuta or not, detail that in any case has its importance in the way Chihaya see people (like following a sort of Karuta skill ranking) so even in how she perceives Arata, we don't know if the true Arata is the Arata that exists in her mind or not.
Adding to it, and that's the last thing, every single time Chihaya and Arata interact, those moments are showed by Taichi POV (or even by his POV), POV that adds a layer that lead us to read them as romantic when it could even not be the case. I'm not saying that they are not, but that Taichi's view is biased and consequently ours.
So, in the end I think it's really impossible to say anything about Chihaya feelings so far, because they do are at an elemental stage. She needs to restore the trio first.