Ugh, Mashiro's way too much of a good girl than is good for her.
I know she means well and all but there's absolutely no reason why she'd need to work so hard to win the approval of someone so undeserving of her efforts.
Should've just kicked the old hag to the curb like Makino no doubt would've wanted to. She already used all the influence to pressure them that she had, there'd be no negative consequences to cutting her out that haven't already happened.
I think it's one of those fiction things. Almost a kind of...power(?) fantasy maybe- the idea that, if we can just show the doubters about how good we actually are, they will come around and realize how wrong they were.
In real life, of course, most of the time toxic people are just toxic, and we really don't "owe" them anything. It's the parents' duty to accept their children, not the children's duty to "prove" that they're worthy of their parents' trust and love.
Sometimes cutting toxic people out of your life really is the best solution. But I guess that's rarely a very literary ending.