Dump her! I did that to a SIL. I also have refused to accept someone that bugs the living crap out of me. She thinks she's my friend. I've never liked her. I'm polite if I run into her but truly try to NEVER run into her. In fact, if I see her coming I cross to the other side of the street.
But still she sent me one friend request that I ignored and then a second with a note telling me that for some reason she doesn't see my acceptance. Umm, maybe because I didn't accept you!!! So I hit ignore again.
Sorry, but facebook is supposed to be fun and not a source of torment.
I say dump her!!!