I think the Catwoman rumor is just something Cher's people are spreading to keep her name in the paper. Putting aside the fact she's in her sixties now she doesn't seem like the type of actor Nolan would put in a film.

As mentioned before, Nolan seems to favor either actors who are talented newcomers (Bale, Ledger, Eckhert) or veteran character actors (Oldman, Freeman, Caine, Wilkinson), either of which will vanish into the role. Cher is neither. She's a "celebrity."

If anything, I'd see Nolan going back Carrie Ann Moss (from Nolan's "Memento" and, of course, "the Matrix" films) if he wanted an "older more experienced" actress.