Wrong. There is no "get out of jail free card" there's only precedent. You give up your planned-out bro trip to sit at her aunt's house in a lame sweater now and you're just setting yourself up to get walked on again later the next time she gets a hair across her ass about something you're doing instead of spending time with her. Soon you'll be asking permission to go skiing every time and begging for your masturbation priveleges to be restored.
Sort of kidding, but not really. Her vetoing your big plans because misery loves company isn't fair. Even if she just wants him to meet the family, shit pick another time when I'm not locked in for the vaca of the year because that doesn't work for me. I doubt the OP's girl is this insistent or bitchy because it doesn't sound like it, but dude... Little things lead to big things. Put your foot down now or forever tuck your junk.