What expenses can my wife and I pay the birth mom in an adoption?

A lifelong friend of ours has a teenage daughter who is pregnant. She is willing to let us adopt her baby but says she needs us to pay her expenses during the pregnancy, as well as all the expenses relating to her labor and delivery. We are fine with paying her medical expenses, but we aren’t sure if it’s legal for us to pay for the groceries, car insurance, etc. that she’s asking us to pay. She lives with her boyfriend and we suspect she’ll use some of any money we give her to support him. What are we allowed to pay for and do we need to put any agreement we make with her about expenses and payment in writing?