Hi J.,I have heard many times of children 'backslidding' in their potty training, so it's not as unusual as you would think. I do know that punishing her by taking her dolls away will probably only make matters worse.
You mentioned that you are expecting again. I could be wrong, but my guess is that you have done a lot of talking about the new baby coming to prepare her. Perhaps she feels threatend by the new addition. Many times when parents are expecting a new baby, the older sibbling feels less important to the parents. New babies are exciting, and causes much attention which is some times drawn away from the one who, up to this point, has received it all.
I would suggest that you key in on the possitive actions your child does, and less on the problem. Give her a lot of praise when she does go, and if she has an accident, just tell her that she's such a big girl that you know next time she'll remember to use the potty.
Tell her that if she wants to, she can help you change her sister or brother's diaper since she's such a big girl... that helps her feel a part of the new baby without feeling threatened and at the same time re-affirms that she's growing up and gets to use the potty. (Sister or brother doesn't get to use the potty yet.)
Use every opportunity to let you child know how special she is to you and that no one will ever take her place. The accidnets will be less and less. Good Luck!