Most of the time they don't ask for corp ID, but if they do & you don't have it you could get bumped up to rack rate.

Usually a company biz card is what they want to see. Back when I traveled for F50-F500 co's that's all I had with me, as my corp id card to enter corp office was back home (some of the corp co's had us use our own cc's; others a corp Amex, so that varied). I don't recall getting asked for corp id when I used to work for the F50-F500s, but I had it if I needed to show it.

The more important question is - have you asked your fiancee her thoughts about using her corporate account & what, if any, ramifications it could have on her if you were 'busted'?

Cheers.