Oh, bull. Eleven and Clara were about an inch away from dating -- they were both infatuated with the other, neither one objected when other people called them the other's S.O. So, yeah, it's perfectly understandable that she'd be more attached to the particular incarnation she had gotten to care for, and that she'd want to change him back.
I mean, it's regeneration -- it's not accurate to try to equate it with Human biology. The incarnation whom she fell for is dead, and this incarnation isn't infatuated with her -- so the psychological effect is going to simultaneously be like a death and a breakup. She has to accept that his old self is dead and mourn him, yet also accept that his new self loves her platonically rather than romantically.