I want my GF to skip a wedding reception so we can celebrate our 1 year anniversary
Why can't you celebrate your anniversary another day?
She's coming with me to my parents in two days. This is the only accommodation I can set up for her.
While your anniversary is important, that can always wait because someone else's wedding is only once in a lifetime. You need to let her go to this important event, or she might regret it and be miserable with you on your celebration.
Maybe you're right. I should reconsider this.
Glad you see it that way. You'll hopefully have many anniversaries, but a wedding is -- cross your fingers -- a once in a lifetime event that can't easily be moved to another day. You're making the right choice.