Lesbian Relationship Challenges Support Group
This community is for those who are in a gay marriage, and the unique challenges that may be had in a same-sex relationship. Find support and talk to others in a same-sex marriage, and get advice from the experiences of other members.
Years ago I was in the same position. Here's how I handled it:
I was polite, reserved, poised. No PDAs, of course. I ignored any covert or overt homophobic/snarky remarks (and this woman made them, trust me). You'll make points for remaining composed under pressure. Grit your teeth and endure it. Let us know how it went.
I don't even know if I have anything to add other than good luck with this and I would be prepared for it to be uncomfortable. Just rememeber that you are doing it for your girlfriend so keep your head up and wear your thickest skin possible.