I might try talking to her, but really, do what's best for your own mental health and family. I would get the bike and send a small gift... and perhaps suggest a casual family celebration when she gets back. I am betting she doesn't want anyone, except the people who will drink with her, to celebrate. I am another person who thinks weddings are kind of dumb to begin with, so probably not the best person to give advice here.
Of course, I have cut ties with all of my dysfunctional relatives, which includes everyone except my dad and brother.
2015 Trek Silque SSL
Specialized Oura
2011 Guru Praemio
Specialized Oura
2017 Specialized Ariel Sport