Nah, she totally wants to win to prove something. I don't remember anymore what if she's told it already. If she was as much against it as you suggested, she would have fought for a while and then let herself be pushed out of the platform to be done with it. But no, she's in aiming for the finals. That means she's not simply forced to fight against her will. She's forced to fight in accordance with her own will. We even saw the flashback with the soldier where he told her she's not ready yet, trying to hold back her eagerness to participate in some deadly competition. Just look at her friends: They are all losers with a slave mentality and probably like you said: They don't have the will to fight for real. But Rebecca totally has the will to fight and that's why she's strong despite her stupid voluntary handicap. She has the will to fight but not the will to cut. In other words she has no respect for the fights. I suppose I can partially understand that considering the whole spectacle is designed by her archenemy, so by offering less violence and less blood she's in fact insulting Flamingo. But is that her real reason?