People associate with you is beause they can benefit from the relationship emotionally or material wise, whether they realize or are unconscious of it.
She lacks self-confidence and projects it onto others. She thinks others look down on her is because she looks down on others to balance out her own shortcomings. She needs others to envy her because she envies others often.
You were there to give her an audience. By dumping on you, she releives the tensions that was boiling over inside her.
You sound like a mature and balanced person. None of the trash that was heaped on you had much adverse effect on you. It's not easy to be dumped on and not become part of it.
To be useful is a good thing, so long as you are conscious of the cost.
