I think you needed to organize this long ago! It's only one week away. What does your contract say for booking time offs? I give a minimum of 4 weeks notice so parents can plan accordingly. I booked my summer holidays over 2 months ago though, so they can book it off with work and not be left scrambling.

Personally I would work the Monday and have Tuesday off since you left it so late, unless you know for a fact that they can easily accommodate the last minute day off. It really doesn't help her to say keep the child home Monday and bring her Tuesday as the mother needs to be at work on Monday and is home on Tuesday.