Pridesmaid
A single lady, participating in an honorary role at her gay best friends' marriage, presumably in a satiny dress they picked out for her; a term fondly coined to mark legalization of gay marriage in New York State during Pride 2011.
Thrice a Pridesmaid, never a bride
Pridesmaid
Slang term for friends and allies of the LGBTQIA+ community.
Let's stop using "fag hag," Pridesmaid sounds more elegant.