Careful with acting this one out, bro....make sure she really understands that she will be losing control completely. I had an ex-girlfriend bother me for weeks to act out a similar fantasy. I finally gave in one night, and shoved her down...pinned her, ripped her panties off and fucked her semi-violently. After a while I let go of her arms, and she started trying to struggle. I thought it was part of the act, so I restrained her arms again and continued. The next time I let her arms go, she scratched my back kinda hard (which she knows I don't tolerate) and sort of punches me in the shoulder. I get annoyed, get off of her, and notice tears in her eyes. I asked her what was wrong, and she goes on to tell me that she was upset when she realized that I was in such complete control of her.
Naturally, I was confused, seeing as how she had requested the scenario in the first place. After further discussion, she goes on to tell me that deep down in her mind, she figured she'd be able to get me off of her if she really tried hard. D-uuuuh! I don't know what posessed her to think that a 130 lb. girl who hadn't ever seen a weight room was going to be able to fight off a 196 lb (back then) guy who trains heavy! But, nevertheless, just make sure this gal understands what she's getting herself into. Personally, I haven't fulfilled requests for rape fantasies since, nor will I in the future.