I agreed to be in a friends wedding. She had been verbally abusive to
me in emails the month before the wedding. I recieved the last one and
had enough. I sent a letter back explaining how I felt she was
treating me, this was 5 days before the wedding. She got mad and threw
me out of the wedding. I had already purchased the bridesmaid dress.
Since she threw me out 5 days prior to the wedding should she pay me
back for the dress? I told her in the letter that I wanted to be in
the wedding, I just think she shouldnt treat me like she had been. Her
emails were very mean.

I believe you already know the answer to your own question. Ofcourse,
morally, she *should* reimburse you for the cost of dress.  However,
legally, I don't think she would *have to* if this was in court.