My niece has depression - how can I help? - long?

The best thing you can do is just be there for her. I currently suffer from bouts of depression and anxiety (as I had a emotionally, psychologically, physically, and inappropriately abusive father and I'm going through a court case to get him out of my life) so I know how it hurts. I've found that you really can't fix depression, and it's kind of a thing that goes away on it's own. The good thing is, she's seeing a therapist, that'll really, really help her (I see a therapist as well) As for what your fam and you can do, here's my advice. Be very kind and comforting towards her and show that you care, but don't try to talk about the traumatic events with her (it'll just re-traumatize her) if she wants to talk about them, she will. Maybe hang out with her a little more and if she starts to talk to you about it, be there to support and comfort her. I hope I helped!