Just how is she FORCING you to have sex? Does she have a gun or knife to threaten you with ? If you don't want to have sex with her, then don't.
No one should ever force you to do something you are uncomfortable with.
I think you should talk to her, explain to her how you feel and if she still carries on like this you should leave her.
I think you should talk to her, explain to her how you feel and if she still carries on like this you should leave her.