Explain to your mom calmly that you think that you should get to go to this party because you can't do it all the time- only once a year. It wouldn't be fair to miss this, and wanting to go to your friend's party instead of visiting your aunt doesn't mean you like her better. It would be nice to go to both, and then you can reschedule with your aunt easily. And even if you can't reschedule with your aunt, you would see her 260 times a year anyway if the fact that you see her 5 times a week is accurate. Tell your mother that. If she still says no, then just say okay. But then ask your mom if you can take your friend to do something special because you missed the party- (If you need any ideas just PM me.)