How to deal with a teen with depression, i never knew ANYTHING she was going through.?

I have four children; ages 2, 15,17, and 24. Well my 15 year old is currently on medication for her depression and i just recently found out EVERYTHING she's been going through. The main thing that concerned me was she was raped twice in her life. I found this out because I recently started taking her to see a counselor and this is how i found it out. Both times by her real father and his friend during the summers i let her go visit. Now i have NO CLUE! what to do because I feel like a horrible parent for not knowning this and having a stranger basically tell me. To be honest, I just thought she was being bad and rebelling which both of my oldest ones did for about a year at her age. What I mean by rebelling is getting into fights at school, always wanting to be alone, don't want me alone blah blah blah but never like this. The reason we started her with counseling and antidepressants was because she tried killing herself one day. Now I need help, I tried talking to her but she just shut down and wouldn't tell me anything and broke down crying. How do I help her? I'm at a lost for once.