Skip our anniversary ?

So today Friday is my sister in laws 29th birthday they were going do her a dinner at her moms house they canceled it and want to do it tomorrow kinda disappointed because tomorrow is mine and my husbands anniversary although there isn’t much for us to do we wanted to do dinner and something special tomorrow with no kids but it looks like we won’t we probably will just go to his sis bday dinner I’m so disappointed ☹️ I was looking forward to this what should I do ?

His sis always misses our parties or comes and leaves early but even if we leave early we won’t have a sitter his mom won’t watch the kids if she’s making dinner for his sister