Another possibility is not that unusual with bipolar folks and that is that she is tired of feeling normal and misses her highs from her mania and is angry and blaming her father for being a part of the crew that supports her treatment from bipolar illness. It is not usual for bipolar to quit taking medication for just this reason. They usually don't have a crew of people around looking over their shoulders so it is much easier just to stop. With Britney she will get push back and won't be allowed that freedom.
It is sort of like a paranoid schizophrenic missing their paranoid fantasies and thus stop taking meds. I have no doubt she is angry about her lack of mania or maybe they need to ease back just a tad on her medication if she is feeling too lethargic.
I am not a psychiatrist but did stay at a Holiday Inn Express last night. LOL. Actually I had a father who was bipolar and grew up learning all of this stuff as he told me all about his experiences as he went through them. He was a compliant patient, but often missed his highs of mania as he felt so very powerful and creative and intelligent, which he was but often this would spiral into mania cycling out into depression and leave him feeling just the opposite. The middle ground is hard for these folks when they have felt the highs or omnipotence.
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You said — I am not a psychiatrist but did stay at a Holiday Inn Express last night. LOL.
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Well, that works for me... :-)