Obviously we don't know the truth behind this incident, but I cannot understand why somebody hasn't stepped in for her. It just seems she is a very desperate and lonely person, and the people closest to her, who you would expect to fight her corner i.e. her parents and siblings, are the ones selling stories about her; it's no wonder the girl needs help.
I don't understand what kind of person (I'm thinking of her record company and kiss and tells) can continue to profit from Britney's misfortune - she is still releasing material yet is blatantly suffering in her personal life which would suggest she needs time off to recover, not to add to the pressure by releasing music, touring, performing and publicising. Somebody needs to step in and take control of the situation for her, but I don't know what person that would be as everyone around her seems to have money as their priority as opposed to her health.
Oh, and in answer to the question, I think she is obviously not stable but she is simply behaving as any desperate mother would who is seperated from her children.
I take the point that she (allegedly) chooses to abuse her own body with drugs and alcohol, but who is in this girl's life to show her the "right" way to behave? It's just so, so sad and as Andy quite rightly points out, it smacks of Victorian freak show.