Featuring the Queen in rom-coms seems an unusual choice, but it was known to happen on occasion. In 2003's American teen rom-com "What A Girl Wants," starring Amanda Bynes as an American High-Schooler who comes to London to reconnect with her father (Colin Firth), she gets entangled with members of the Royal Family along the way . . . naturally.
Admittedly, the Queen doesn't have a huge part at all, but the film provided a cameo of Elizabeth Richards, an impersonator of the Queen. This would be one of a number of occasions in which Richards stood in to play the monarch.