Well I think that Anna has to be part of the Elite 4 or be the champion because I'm fairly certain they're the only ones who are supposed to have any legendaries on their team. Given that her brother Noel carries around a Clefable doll and has Clefable as his ace, I'm assuming the situation is the same with Anna and her Jirachi, meaning that for her to use her Jirachi in battle against us, she'd have to be Elite 4 or Champion. Also, everyone else in that group is a gym leader or (ex)Elite 4 so having Anna just off to the side doing nothing would be strange.