Despite what she claims, Faith has changed and evolved, she isn't the person we first met in the series. She is still haunted obviously by that past and her upbringing but that is again only natural, just as Angel has been haunted by his and continually trying to make up for it. It is very remarkable to me though what a great duo these two are for one another.
That shouldn't be a surprise. IMO, Faith was always the best mirror for Angel's search for redemption, going back to "Five by Five" & "Sanctuary." "Sanctuary" is really the quintessential Angel
episode, since it's a story that you couldn't do on most other TV shows; certainly not on Buffy.