I agree that Mimi would be an excellent match for your group, but perhaps she just prefers to do her own thing. Still, the occasional team-up would be nice, and you could work that into the story with her sort of being like Batman to your Justice League.
Also, have you tried posting to Mikazuki's Amazonia forum? It was initially intended to be a female-only FMG roleplay board, so it still might have a considerable number of female members who would be interested in this genre.
http://amazonia.moonwarrior.com/index.php?action=forum