Kitty is not expecting anyone to understand her if she speaks like this - her cat form can only speak cat, after all. Sure, under normal circumstance she could cast a telepathy spell and speak to the other person that way, but... Yep. Tough luck, for the same reason that she cannot wander around in a much more practical for talking human body right now. This place has severely dampened her magic to a point where it is essentially unusable, particularly down here where it seems completely gone.

So she doesn't even try to respond with words and just wanders over to push her head against the hand, rubbing her scent on it while getting a whiff of Susan in turn.

...she's been here for a while, hasn't she? But, more importantly: Does she seem dangerous, and does anyone in the cell seem dangerous? Because Kitty, being a cat, could fit through the bars but has no interest in going into actively dangerous territory, interesting as it might be.