I don't think Mandisa's size will hurt her.See Ace: Bottom 3 two weeks ago.
People (in general) are not voting only based on looks.
BESIDES: Mandisa is really lovely.
Witness Ryan being rather flirtatious with her. Taking off her shoes...very sexy. Last week he was also very flirtatious. His manner with her is very different than with the other female contestants.
Now this may just be because she's the first real woman to make it this far (as opposed to a 'girl'), giving Ryan more leeway to act like that.
OR, it may be that she's a very sexy woman that inspires that kind of behavior. It happens, even with larger women. (Believe it...or not.)
But watch Ryan tonight...see if it continues.