Tsk, tsk
Death, you should be paying more attention if you missed out on something like this
Just kidding
, Rika went to the Sonozaki House to deliver a huge jar of Soy Sauce she had in her house; later then Shion(passing as Mion) probably was the one to phone Satoko at her house and say that Rika had dropped by and was having dinner here, thus asking Satoko to drop by and join them.
Which was the reason why Satoko left 2 meals in the fridge.., something that she had done for when Rika returned.., but since Rika was "having dinner" in the Sonozaki House and Satoko herself was then asked to join her..., she naturaly went along and saved the food for later.
Remember.., Satoko doesn't know she had met Shion ever before, she only knows Mion.., and the real Mion doesn't have "that grudge" against her as Shion does..; Thus naturaly to Satoko.., Mion is her friend, so she had no reasons to be afraid on not to come join them for dinner..; specialy if Rika was there aswell.
Its all in episodes 7 & the begining of 8, you can't miss it
