AITA for canceling $14,900 worth of plans after my niece ruined my daughter's school show?

During my daughter’s end-of-year show, my niece grabbed the microphone and poured glitter glue down the white dress Harper had practiced for 3 months to wear. My mother laughed and said, “I promised her a MacBook if she made Harper cry.” My brother kept filming. That night, I canceled $14,900 worth of plans I had already paid for. The email at 7:40 the next morning made everything worse. ---------------🦦Otter Stories🦦--------------- #reddit #stories #redditstories