Perhaps its safe to say that ririka on some level resents that she doesn’t have an identity and on some level she has that 1% hate on the wrong person which is her twin. She may be able to copy kirari but she definitely doesn’t understand her 100%
Oh, absolutely. I think it's entirely fair that Ririka might have resentment towards Kirari or even hate her a bit. I'd even go as far as to say her anger and venom towards her sister is excusable — at least right now in the beginning stages of her finding her own identity, where she's been thrown off balance.
And totally agree that, as much as they were able to copy each other perfectly, they still weren't actually inside each others heads. A super obvious example is that Ririka clearly doesn't have the same affinity for Sayaka that Kirari does, and has shown — at least once — that she didn't understand just how deeply into Sayaka Kirari is. That scene where she's about to leave on the helicopter and she calls Sayaka a nag is either 1. Ririka acting in a way she thinks Kirari would respond and missing the mark completely or 2. Ririka briefly showing her own opinion of Sayaka. Either way, she was still blended with Kirari at that point, but failed to respond to that interaction the way Kirari would have.
Also, Sayaka's intuitive ability to tell them apart must've been terrifying for Ririka. Her role in life, from birth, was to be Kirari. And then some random junior high school student comes along and somehow picks up on the fact that she isn't Kirari. Talk about an identity crisis lol.