i said this a few times, but, i think Jean should be diferent, she should have a dom/sub personality mechanic. imagine this:
xavier ask us to help someone he holds dear, another psych who is losing control of her powers, thing is, she is actually possessed by the phoenix, so we could "help" her by either, subduing the phoenix, making her more submissive, OR, letting the phoenix out, but making her more of a dominatrix.
in truth she would end up as 2 characters, and as you progress with her, you could make her other side come out or go away as we want. it could go as far as something like, phoenix is out, giving us a BJ, but then you "seal her" bringing Jean out, and she is doing it without knowing why! so it could work like those hypnosis stories.
i will still defend that, each character should have a unique mechanic associated with them. and Jean having split personality would be perfect!