My sister scheduled my niece's birthday party on the same evening as my daughter's first ballet recital. So no one in my family felt like they could go to my kid's recital. I had bought tickets for some of them (not my sister) prior to my sister's announcement. We were excluded from this "family party" because we had this prior commitment, about which everyone in the family were aware. My sister "forgot" about the date and then wouldn't change the date of my niece's party. Our children are close like siblings. I'm furious with my sister. Upset over it all. I feel bad for my niece and for my own girls. I let my sister know and she thinks that I'm being petty and selfish. I am wondering what others would feel about this. Am I being ridiculous?