People cannot change after 20-21 right?

IE. when a girl from the poor areas marries a rich guy, even after years when she meets with ordinary people, you can see the real her coming out and that when she is around the rich guy and his friends and family, she fakes everything from accent to attitude. and when she argues with the rich guy, the refined, fine woman goes away and the ghetto thrash comes swearing and behaving uncly.. those mean she hasnt changed, but is only faking it. is this about not being able to change no matter how much she wants it, or is it that she doesnt want to change completely...