I really don't want to offend anyone, I did put up the trigger icon just in case, but here is my 2 cents:

It is possible that your sister is having a manic episode, but honestly, every time I change something in my life my family thinks I'm having an "episode" and it's just not true. When I left my husband, I was not manic. I was actually pretty stable at the time and finally thinking more clearly and realized I had mostly been staying with him because I had been depressed for so long, and I just didn't have the energy or motivation to leave. When I finally became more stable for awhile, I could see that there were a lot of problems that I had been ignoring, and it was best for me to leave. I cut my hair short and dyed it black and changed to a more "punk" style. I switched to a new therapist. I started going out more and having some fun. None of it was because I was manic; I was finally feeling good (not depressed and not hypomanic) and was ready for some changes. My family was shocked, because I had never told any of them about the problems I had with my husband because I was too embarrased.

I know you are just concerned and want what's best for your sister, but if she has never even been diagnosed with bipolar (and if she is on Zoloft I imagine she has already been seeing a doctor about her problems with depression) then it's possible that she is just making changes in her life that she feels are necessary. Of course it's not right that she's been cheating on her husband, but plenty of people without bipolar cheat on their spouses. People without bipolar (i.e. my sister) change jobs when they find something new they would like to do. And the rate of divorce is quite high either way. As for the nose job, you said you weren't sure how she paid for it...is it possible her boyfriend helped pay for it? Or she may have been putting money aside for it for awhile?

I AM sorry if I have offended anyone, this really touched a nerve with me because of my own experiences.