Frustration

I don't know how my stepdaughter does it. She spoke to her bm and was told that bm was sending her $50 to spend. This was two months ago. Bm does this all the time. Bm tells her she is going to do something and the backs out and always has some excuse. Well as checked the mail the other day and there was a money order for her for $50. Only took her two months. Why does she tell the kids that she will do something with no intention of following through? I get so tired of seeing sd disappointed because her bm lied again and we have to follow through with it for her. We are so tired of her not making the effort for her kids unless we make the effort for her. She has three kids and has never done anything for them. Someone asked her one day why she doesn't see her kids and she answered because my husband and I won't come get her. Since when is it our responsibility to be her taxi to see the kids. She is older than we are. She needs to grow up and take care of her responsibilities.