Most Helpful Girl
She still feels comfortable with you... there is a history. Seems like she wants everything HER way. She broke up with you and now she is calling the shots on sex. What you need to do it tell her 'no'. I am sure it will shock the hell out of her, but if you want to gain the upper hand and not look like a pushover you're going to have to do it. Then wait for a bit and see what happens. I believe she will get upset and angry at your rejection of her, but she did break up with you. Do the right thing and tell her 'no'. Stand up for yourself and grow a back bone.
Most Helpful Guy
If you're feeling vindictive. You could just use her the way ages trying to use you. Getting pleasures until she decides it back then cling it quits. That would show her. Better off just ending it though.