| Need Your Help

Yes, I have a little life dilemma. I would love your opinion, so here goes...here's the situation: I am away in the city (a few hours south of where I live) helping and supporting my cousin open her new floral boutique. I had made the decision to be with her for 10 days or so. I was going to go home next Tuesday. Today, I found out via s.o.s. phone call from my daughter that I had apparently promised my Mom that I would help her set up and run her garage sale this Saturday. I have absolutely no recollection of this date for the garage sale and it isn't written in my day planner (trust me everything is written in there) - I do remember a conversation on a few occasions about her (Mom) wanting to have a garage sale, but I honestly don't remember the date. My Mom is super disappointed and my cousin was counting on me to be with her for the next 5 days - lots to do to open a new shop - What should I do?