Some posters seem to either have not read the post properly, or are deliberately misunderstanding. They're talking about MN 'double standards' and how people would give a different response if it was a woman asking.
I've been on here a long time, and that isn't my experience at all.
My opinion (and I believe most posters, based on experience) in this sort of case is:
She is a grown woman, away on holiday, celebrating her divorce being over perhaps, with her friends...... noone has a right to give her a curfew or to suggest that being out at 5 in the morning means she's cheating. The fact you think you can trust her until 2am but after that she must be cheating on you is illogical, and probably says more about what YOU think you'd do in her shoes.
If I was your gf and knew that you didn't trust me and thought I should have a curfew, I would get away from you as fast as I could.
The occasions when people have objected to someone's partner staying out til the early hours have ALWAYS been in the sort of situation where: they are staying out til the early hours / coming home drunk when they're meant to be looking after children the next day or out on a family day. And they end up staying in bed and shirking their responsibilities. Or they often say they'll be home at 10 and come home hours later, without a message to the Op, who's left worrying if they're OK. Or they don't let the Op go out for the night, but they disappear out 3 times a week themselves.
This situation is completely different. A woman, on holiday with her friends, doesn't have to answer to her bf back him. Can you imagine being 47 and saying to your friends 'I have to leave the club now. My bf back him will be upset and angry if I stay out beyond 2am'.