And yet she retained a heroic persona? Either they forgot she wasn't heroic to start with and only changed due to Carol, or she was so permanently changed even being "cleansed" wouldn't revert her mind.
I haven't read the actual story where it happened, but all the references I've seen to it in other comics implied she turned good because Xavier helped her see the light while he also helped her deal with Carol's personality in her head. Not that she was just irredeemably evil until carol's goodness rubbed off on her. Hell, they even used the carol personality in her head as an evil villain that had to be stopped once, so how would that track with it being the only source of her goodness?