Unless we work out a better idea, it might be for the best to stick with that point. Whatever you have Mesprit do is totally up to you. If we were being exactly-perfectly-canon-stickling, then she'd sit in Lake Verity doing nothing until Dawn came to visit, at which point she'd be all "LET'S PLAY TAG WHEEEE" and commence roaming, so... it should be okay to cut straight to the roaming part.