[andrewas]

Jaheira's polymorph has no effect on enemy reactions to her, the only advantage it has is that the bear forms are more powerful that Jaheria in human form is (At least in theory, IMHO jaheria at higher levels is far better).

TO fix the crash on returning to human form you need to replace on of the .bif files. Dunno which one, its the one that contains the spells. Probably the easiest thing would be to reinstall the game.