I agree with PP #1 talk to doctor asap.
AFAIK you shouldn't try and LOOSE weight while pregnant but maintain and/or keep to a smaller goal than "normal" pregnancy. I think most doctors recommend 15-20lbs weight gain but ti really really needs to be discussed with her doc for that decision to be made.
There are a lot of good prenatal work out dvds out there, espeically yoga which can help a lot with labor!