Occasionally I'll fly w/ my sister somewhere & have managed to get her upgraded. Always wondered what would happen if I could only get one upgrade & there were 2 of us. On the one hand being a spoiled FT princess I want to be in C or F. OTOH, said sister doesn't fly that often & if I was a good sister I'd let her have my seat in C or F. Wait I am a good sister - I've given her Int'l F Award tickets as birthday gifts. Phew. But still I haven't sorted the dilemma of what if only 1 upgrade is available. I'm leaning a wee bit toward me taking the F as she's just my sister

On a trip a year ago said boyfriend at the time & I were flying LAS-LAX, me being elite & him not. Since it was TED no upgrade so no worries there, but him being non-elite he couldn't get E+ & I was really dreading E-, but figured I'd do the right thing & sit back there w/ him. I know it's only an hour, but hey it's E-. Luckily I got a UA agent who was willing to bend the rules a bit & put him into E+. Good girlfriend crisis averted!

Re: the OP's friend's situation. If it was a vacation & the girlfriend (or if it had been boyfriend; gender irrelevant) had never flown F, then yes the right thing to do would be to offer up the F seat to the other. It would have been a treat & a great way to start out a holiday. I think he should do it on the return since he didn't do it on the outbound, but given there's a bit of argument about it probably is going to take the luster off the gesture for both of them. However, it would still be fun for her.

BTW - on a biz trip to LHR w/ a client I used SWUs to upgrade to C. He had no status & I wasn't willing to use my SWUs for a new client (hey, they're hard-earned), so he stayed in E. Turns out he tells me on the connection LAX-EWR-LHR (so about 6 years ago when UA flew to LHR from EWR) that his credit card has a self-imposed $500 credit limit and he doesn't have a company card. So I had to call Diners to say expect an unusual high charge but to please ok it, as I'd be paying for 2 hotel rooms and all the meals. I was furious that he wouldn't have made arrangements w/ his company to have the hotel prepaid or gotten a company card, and that he waited until the connection to tell me. I then felt no guilt whatsoever about him sitting in E! And he checked out of the hotel earlier than I did, so I didn't find out until checkout that he had a bunch of porn films on the bill (which I obviously couldn't bill the company for & which he never reimbursed me).

Cheers.