I'm not sure, but you have the package "useMagic" but I think it's "shout." I've only ever used ai to force an npc to shoot at practice dummies. What if you just add a quest with one line of dialogue that says something like, "cast rally, please." and she replies with some generic dialogue like, "I understand." Or use XVASynth to write/record original lines. Anyway, the dialogue can end with a script fragment that forces the follower to cast a spell.