I wouldn't say that that was undermining her character at all. She spent that whole sequence being creeped out and defiant and telling him to go get his cheap titillation somewhere else. And then by the end she's strangled him with her own chain in a classic display of badassery.

And really, put it in context: no character was doing awesome at that point in the movie. The droids were basically abused slaves. Han is stuck in a watery cell, blind, and feeble from hibernation sickness. Chewie and Luke are only slightly better off: they're in the same cell but with no hibernation sickness. The only character in any sort of advantageous position was Lando, who was undercover.

Was Leia's slave outfit a bit of obvious fanservice? Yes, clearly. But did it undermine her character? No, I don't think so.