Gotta say, to me Runa feels like the most normal teenager out of the quartet. She has a pretty good sense of social awareness to understand her circle's mood, much like Tomita's, however she doesn't have the security to express her real thoughts so she tends to internalize them to fit in the group and not being seen as an outcast.
Right now, Runa has two problems: her struggle of her self identity and Kanae. The first one is something almost everyone goes through, separating her childhood likes from her mature ones and choosing which ones she wants to show to the world. She still likes cute things, but she doesn't believe they fit her anymore, she's self-conscious about them and thinks her friends will mock them and make fun of her for using them, so she hides that side of her for the sake of her social life.
The second one is much simpler but also more tricky to deal with: she doesn't like Kanae. From her inner thoughts it's easy to see that Runa considers her a selfish, self-depreciating girl who only wants for others to lift her up, a very accurate perception. If it was only her, she'd prefer not to deal with Kanae at all, however she's now part of her circle and unfortunately she has to now. Any attempt to point out her discomfort comes with the risk of discussion, therefore endangering her social status and the possibility of being left out like Ichika, so she has no choice but to shut her mouth and bear with Kanae, no matter how much she dislikes her.