True mental illness tends to demonstrate itself in the late teens and early twenties, just a function of growth, age and maturity levels. This child has had "mental illness" diagnoses all over the place, sounds like from a very early age, yet no serious action has been taken to make sure she takes meds. A lot of what is being described is nothing except some very obnoxious behavior, such as beating up her brother on the bus, threatening her parent with a knife, cutting herself, trying to choke herself????(I must admit, this one sounds very strange and dramatic to me, and I've seen a lot!) But we can't sit far away from this situation and try to figure out anything until the OP comes back, if ever, and provides more information. We're already firm on that she can't put her child up for adoption.
These behaviors are not simply obnoxious, they are indicators of some potential very serious mental health issues.
The teen is a danger to others, and probably a danger to herself.
**the trying to choke one's self? It can be used as a type of "high"---you've gotten a "head rush" before?