What Steps Are Required To Deal With Suicidal Tendencies In A Depressed Person Suffering From PTSD?

My daughter is 17 and is in extreme need of help. She has been diagnosed with post traumatic stress disorder and depression. She has attempted suicide many of times and has runaway a few times.She has had problems with bullying and low self-image. She has self harmed by cutting. At times she can become very angry which cases her to start hitting and kicking. When angry she will also scream and yell and throw things at no one in particular. Then there are times when one minute she is angry then in a second she goes to happy and laughing and also the other way around (happy to angry). She has been placed in a special school for kids with behavior and emotional problems due to the fact that she was baker acted 4 times from her regular school because of suicidal thoughts and attempts. She has been baker acted 8 times from home due to being suicidal, running away or becoming out of control. at one point she spent almost a month and a half in the hospital while other visits have lasted anywhere from 2 days to almost 3 weeks at a time. She is on an IEP. Now, some people say she might have autism but i am not absolute sure about it. She dose have some of the signs of it but if she did have it wouldn t she been diagnosed when she was a lot younger. If you could please help me i would greatly appreciate it.