Tired of being the mature one

Alright ladies, I kinda just need to rant right now.

So there's this lady that is interested in my fiancé. Recently she's tried telling him that she saw me out running around with another guy (only people I really spend time with are family, my fiancé, our roommate and that's about it) until he described me to her. She proceeded to try to get simpathy for the misunderstanding but failed at doing so, so instead she started to cry and ran out of the house (mind you this lady is 30 something, 3 kids and divorced; my fiancé and I are 19 and 20, no kids -not that we don't want any LATER- and ENGAGED).

Well, my little brother works with her but I don't think she's quite realized that he's my brother. I had my brother just simply mention us (fiancé and I) to her and she had the audacity to call me a whore and him a "bitch of a boy". All because he won't sleep with her and has turned her down everytime she makes an advance towards him. Now when my brother told me what she said, of course I was angry because here's this lady that knows nothing about Jesse (fiancé) and I and she has the nerve to call us names as if (1) we aren't friends with her ex-husband and (2) very unavailable to other people in that way.

I was told to forget about it and be the bigger and more mature person, but right now I want nothing more than to cuss her out amongst other things (I'm generally not a nice/sane person when you piss me off). Is it wrong that I feel this way??

It's just so frustrating, I'm already stressed from wedding planning, working, and trying to find the time to fix my car. I'm getting tired of being the mature one, all I want is to go bridezilla on her.