A genie's magic is Cast From Life Span, to an extent - they can die if they overuse their powers on a broad (read: "global") scale for too long, presumably at the behest of their master. It is heavily implied that the last known genie to suffer this fate was Eva Braun.
Comedic Sociopathy: Jean has little regard for the consequences of her actions unless they come to harm herself. Had their situations been reversed with Neal becoming the female genie, Jean would have been only too happy to use his wish to "do" Neal. She turned a nerd into a girl and later chose not to turn him back due to more concern over her own problems and possibly even spite. While her reason for turning a ship captain into a woman was understandable, her Disproportionate Retribution against a friend of the captain was less so. She regularly abuses people, especially Neal, for her own needs, without any respect at all for theirs. This trait of hers is usually Played for Laughs.
Failure Is the Only Option - As with all comics of this type, Jean will likely never be changed back no matter what she does. Made blatantly obvious by the fact that her powers are best summed up as 'can do almost anything except turn herself into something other than a genie'.
Well, it only makes sense that the one thing she can't wish away is the very power that allows her to grant wishes in the first place.
Neil has called Jean out on it though, and literally ordered her with a list of demands to try and set things right. Whether she actually does or not is another matter though, but this is the first time since the comic began that Neil has really stood up to Jean.
Neil himself is no saint, either. The second time Jean transforms him was because he made a tasteless "period" joke. You don't say things like to a woman, especially one that was a man. He has also said some other pretty ignorant comments. Really, sometimes Neil asks for it.
There's also a good deal of Hypocritical Humor inherent in Jeanie's Irony Blindness, since all Neil is doing is living out Jean's own Genie Master fantasies.
Jerk with a Heart of Gold - Jean, though given his situation it's understandable that he's not taking it well. Jean may be a borderline sociopath, but he does try to do nice things sometimes, like when he/she brought breakfast to Neil once and helped Neil turn into a man again.