Why is my budgie bird so aggressive?

every time i try to pet her she freaks out and bites my finger. why? she never likes to sit on my finger and even when i feed her she bites me. it feels like i'm being pinched by pliers! don't give me any of that "budgies get bored and you need to give her toys" crap. she has lots of toys and i move them around to keep her amused. but she is just so mean! she even killed my other budgie bird. what can i do to keep her from being so aggressive? if i can't, should i have her put down?