I don't know how you can pull off Catwoman in this "Nolan grittydark universe".
Catwoman is probably the easiest Batman villain to do in this style of Batman story. Certainly far eaiser then Ra's al-Ghul.
'Cause she's got no superpowers. When it comes down to it she's like Batman only a woman, a different choice of animal motif, and (typically) less scruples as a vigilante - the last point giving you your point of ethical contrast. Catwoman is the avenger Batman can't be. Cue ideological debates where Batman growls at at a woman in a catsuit and that's a wrap.
Definitely easier then going:
'Yes, let's do a down-to-earth Batman movie -'
'- Where he fights an immortal Arab!'