So Tenley isn’t really a bad guy in spite of all she goes through in her life, right? What kept her from just going full evil?

Well she does go a bit mad for a while seeking revenge, but there are several reasons she hasn’t become completely evil and just lashing out and everyone and everything. First, besides fighting her mom was fairly useless in every aspect of her life which meant that Tenley early on had to be the responsible one in that relationship and take care of both of their needs – even later when she calms down a bit she sees it as her duty to look after everyone even when they do dumb stuff. Also she’s quite imaginative, reads a lot of books, watches a lot of shows, and probably that escapism has helped keep her stay strong.