Stress and pain causing Aurora to form a brand new personality has at least one example of happening before.
The underrated WEAPON X series by Frank Tieri had Aurora develop a third personality completely different from Jeanne-Marie or Aurora. This was a reaction to the sudden beating her lover Malcolm Colcord gave her combined with a violent coup at Weapon X by Brent Jackson. (Malcolm, already nutty, went extra crazy after Jackson called him a "mutant lover.")
Aurora helped Colcord and Madison Jeffries escape, but the third personality (much more violent than Aurora had ever been) beat the hell out of Colcord (at superspeed) and left him and Jeffries stranded in Canada.