Sounds like she is Bipolar: happy one moment and then all banana balls the next. There's something going on in her head if she flips out when you try to be nice to her. Anywho, if she flipped out just because you were being nice now, be glad you found out so soon before things got serious. She might have done worse things had you two gotten more intimate and married.
Just hang in there, Mirabilis. You'll find the one for you.