I love Yumi, but what I don't love is justification of ehr behaviour as "tough love". It really isn't. Yumi lashing out against everyone, but Futaba make herself an easy target, so she gets the worst of it.
She's easy target because, while her weight isn't a problem in itself, it's an easy vector of attack for Yumi, jokes kinda write themselves. It's als easy to see an immediate effect Yumi's words have on Future. Yumi hits, Futaba immediately bleeds. Easy pray.
For Yumi live is a fight and she's in a losing position by default, so she resents Futaba for not standing up to her, for rolling with punches. Even worse: Futaba's half-hearted attempts at being a bigger person just make her a bigger target, no pun intended.