Happy birthday to your mom! Special occasions are much more special to me now that I am sober.
Dee always has good direction.
My plan would be to have something to drink always, to have an "ally" in the group (even if just someone to exchange a look or such with- for me it would be my boyfriend), excuse yourself to take a minute and go to the bathroom or whatever if you feel overstimulated/frustrated/etc - and give yourself permission to politely leave early if you start to feel disturbed.
I always remind myself that it really is just one [ ] and even if it seems like the "only" time this or that - and of course it is, in this case- it's still not worth my physical or emotional sobriety. No matter what or who is involved.
You can do it.