My mother in law is ridiculous

I love everyone in my husbands family but his mother and father are difficult to like sometimes. My daughters birthday is coming up in a few weeks and I wanted to have a simple birthday party for my husbands side of the family since you can’t really throw a big one right now due to covid and since they live an hour away from us. I discussed the date with mil and she said that date was fine but apparently she wasn’t listening or forgot so now she is insisting on throwing the party on a date we can’t attend to due to other obligations. She claims this is the only day all month she can take off even though she is self employed and she normally takes off Sundays during tax season (she’s an accountant). My husband and I have been arguing about his mother’s behavior but he refuses to confront her. She has only attended my daughters first birthday she’s five now and this is her only grandchild. Am I being ridiculous for being upset by this?

@Briabella I would but she says this is the only day she can do it and I have already made prior plans because we previously agreed on a different date. We have a busy month the entire month of March so it isn’t as easy as rescheduling the dates

I personally don’t care if he isn’t able to come but my daughter is upset that one of her grandmother isn’t coming to her birthday. She even said granny doesn’t love me 🥲