Welcome to FT! The GA is who you should've have asked, not the FA since the GA is the one who assigns seats and makes the change. You were both on the upgrade list, she cleared - you didn't. You could've said no, thanks and take your chance on whether you can get the original seat back (GAs can be unreasonably rude if they are asked to reverse the upgrade, even though they should've checked if you wanted the upgrade if only one of you cleared) OR your fiancee could've come back and offered the guy in her old seat, the F seat instead so you guys could sit together. The bummer of the latter case is that you "paid" for the upgrade which is no fun.