Have you discussed with her frankly how you are not interested, just want her to be your friend? If you have only hinted and/or given in and participated, she is free to ignore your inconsistent behavior or hope you will come around after awhile. Take away her options for manipulating you with deliberate words and not allowing her to continue when she starts a sexual conversation. I would try that before I blocked her completely, especially while I looked around to see if I could find more friends both online and in person so I wasn't so vulnerable.