The show made it seem like she was in love with Mugen or Jin, who in turn had no interest in her which often made her upset. Judging by their interaction on the show, I'd say Mugen is finally giving her the attention she wanted, but it was more than she was ready for. My call...didn't start out as rape, but...
Then again,considering the hold she has around his waist (as evident by the interlocking position of her feet behind his back) The evidence points to nothing short of consensual(sp?) sex.