First off: This is a throwaway because my friend knows my normal username

Anyway, I'll keep it short.

My friend's sister has a HUGE crush on me. She recently got my number from my friend (he swears he didn't give it to her, but come on) and won't stop texting me. I've told her I'm not looking for a relationship or anything, but she just won't give up. I've tried ignoring her, but then my friend gets mad because she goes to him to complain. Then I've tried acting pretty vulgar in the hopes that she'll be disgusted, but she's either down (if I talk about sex), or thinks I'm joking and flirting.

Anyone deal with this before?