That shows respect for your time and gives you an opportunity to say "yes or no, I have plans". If she wants the job bad enough she will make other arrangements for child care.
But it isnt her job to involve Chris in the decision making. That time is passed.
It IS her job to arrange childcare for when she is not available during her scheduled time. So if Chris cant do it, it should be on her to find alternative care. I believe what she needs to know is that you arent always going to be there when she is in need. Backing out of your GAL plans to help her out is a choice you can make - but it sets you up to be the on-call babysitter.
