Advise please.

Let me set the stage. W wants to get her hair done this weekend and has to work, D has Saturday school. She just asked me if I could get up to take D to Saturday school. I told her I was going to work some ot this weekend. I need to pay a retainer.

She then got an attitude saying that she wants to get her hair done and she has to work and I should be able to pitch in. I bit my bottom lip but I wanted to say if I can't be trusted to have her in the house by myself this weekend, assuming someone other than her said that, how and why should I be expected to run her around. Get that cop friend of hers or the cart boy she was in the car with to help out. I'm sure he's willing to do something other than to jump her bones.

My question, would it be childish for me not to help out or should I let her get used to not having me to do things she has taken for granted??