Doesn't matter what slot you have something memorized in - charm will use any spell you have out - particularly if it is offensive =)

I got swarmed by a group of 3 charmed ones once - I do have to say it was most humorous (course I was old enough to stay alive)

If a party member of yours does get charmed - I recommend root and run if they could kill you otherwise =) It is best NOT to kill your own party members - tempting as it may be if they are obnoxious *winks*

~Siren