You could tell her that you heard he was going on vacation that week.
I have to say, I'm lucky when it comes to my mom and shows. She knows nothing about any of them, so she trusts me completely.
Although, Mamma Mia is still her favorite and if we had enough time, she would see it on every trip.
Finish each day and be done with it. You have done what you could. Some blunders and absurdities no doubt crept in; forget them as soon as you can. Tomorrow is a new day; begin it well and serenely and with too high a spirit to be enbered with your old nonsense. ~ Emerson