I'm glad to hear that the situation with your daughter has improved slightly. As for her symptoms of bipolar disorder dissappearing and reappearing quickly, it's possible with rapid cycling BP but I think your situation doesn't quite fit that criteria. From my experience with people I know with this condition, they typically change through an entire cycle of rage, despair and repentence, and rapid uplift again until anger. If your daughter fit this criteria, I would expect her to feel terrible and depressed after hurting you and then doing it again.
From your postings, it seems like her "symptoms" are being primarily based off of violatility. These "symptoms" coincide well with mania in BP disorder or just before sliding completely into depression. However, I would expect her behavior to follow more of a circular pattern unless she's BP II. Either way, while I've heard of long term periods of mania, they are pretty rare because most people eventually become psychotic. Psychotic behavior is quite noticeable and will probably require hospitalization or antipsychotic medication.
If Bipolar, your daughter will probably not have complete control over her condition. Heck, most older people who know what's happening still have a tough time completely dealing with these things. My point is, I wouldn't expect things in your situation to change much by giving in to your daughter's wishes if she's Bipolar.
The problem is, even getting what you want when maniacal doesn't really seem to change the "symptoms". Different things in your life influence BP disorder, but the condition really changes your perception of reality. If your depressed, having something good happen is not going to make you bounce back. If maniacal, having your family's empathy or support won't cause real short term improvement either.
If things are getting better after making this decision, then I would be reluctant to attribute her actions to BP disorder. Your daughter does seem to have "control" over her actions at this point. This is reiterated by the fact that she is doing better because you granted her wish. Maybe things stem from something completely different or from other tribulations of adolescence. Its something to considering anyway as I wouldn't expect her to be in control or to make an effectively calculated change like this if exhibiting BP symptoms.
Good Luck and I hope her improvement continues,