Stop letting her make you feel guilty. Call her on it, when you realize what she's doing tell her about it.
I think it depends on her age and maturity and how she feels about you. I think you should definitely sit her down and explain her feelings my husband and I do this and our relationship is so much better. You have to have communication. She may be hurt if you are spending too much time doing something else and not with her or the baby. But she should be a mother and not use her child in that manner - that is wrong!
Tell her how extremely immature it is to use a child as a bartering tool. Adults should never bring children into their own adult problems. In the end, as the child grows up, he/she will be the one most effected by being a pawn in the middle to 2 people that can't get along. Sad, she should know better.
Start respecting her.
Answer
The fact it can be used as a guilt trip suggests it wasn't wanted in the first place. Don't get people pregnant if you don't want the responsibility.