i keep thinking did she need someone strong to help her
Nope. But my ex made sure I knew that the new guy, whoever it was at the moment, was better at handling her. But that is a lie. That's to keep me down and pass blame onto me. Plus, they really don't see how they are (or won't let themselves see how they are), so of course it looks like things are going well at first. They are still in the idealization phase!
And they are notorious for making it look like they are so happy and so much better off once they leave you. But you have to believe it will happen again. They *have to* believe they are happier and better off. God forbid they face the loss, the guilt, and the shame. They need to feel like they are the winner and you are... .well... .you are maybe just the loser. But that's a lie, too.
did she need a better situation like work or school to help her feel better
Good lord, no. After all the things I did for my ex, I finally realized that you CANNOT fill a black hole. But boy, they want you to believe that there was something YOU could have done to make it all better for them, or some situation that was to blame for their misery and acting out. As long as they find someone believing that lie, they will get to continue to push all of their garbage off onto them. But that's not the truth. Those are excuses for their behavior. Think about it... .who couldn't find SOMETHING in the current partner or current situation to blame for all of their garbage? Anybody could. But it would just be a scapegoat so as to continue down the same path of destruction.
Aren't there things she could have done to make it better for you? You aren't her hero. Only God can be someone's hero. Are you God? Of course not. Relationships are not supposed to be like that. They are supposed to be mutual. Two whole people coming together to mutually love and partner with each other and help carry *each others* burdens. Not one-way. Not "do everything for me and make me happy." That is the BPD lie.
Have you ever read this article? If not, you need to. It is what happened to you, and it is what is happening right now with her and her new guy. She'll wreck him, too. She will. This is truth. All of that "If only I did this or that... ." is not the truth.
https://bpdfamily.com/content/how-borderline-relationship-evolves