As a minwu user/abuser, I think it's a good thing she don't heal at 50%+ health because she can only use it 4 times. If you want her not to spam the same buff over and over again, make sure the whole team get the buff on her first attempt to cast it. And you want to pair her with a tank, that's for sure.
This is what I'm getting at. I'm running her with Esther and Cloud. Even with all ATK spells and def/spr buffs turned off, she prefers to run towards enemies rather than buff them with Lightning ATK/Debuff Res/self activation down.