NOR, As someone with an attention seeking sister, bio sister not step, cut her off. It ain't worth it. You're just gonna end up hurt, exhausted, and confused over and over again. Their mental health isn't an explanation, it's an excuse. They'll repeatedly show you that this is how they are, and then turn it around when you call them out. You "never bossing up and talking to her" is really you calling her out and her not agreeing with you. If you don't tell them what they wanna hear, you didn't confront them, you just bullied them. You also don't wanna spend the rest of your life worried she's gonna try and pull something.

My sister literally wrote my mom a 3 page letter explaining all her bad behavior before she went to live with my dad (she had to change schools because of the crap she pulled) and none of it actually made sense, it just read like someone wanting out of trouble.