Well, I personally wouldn't ignore the roll play, because it is a great way to use her imagination and it is part of communicating at that age.
I would just let her direct the roll play, and let her indicate what she is and what you are during play. Little kids can go through a lot of thoughts very quickly and it may just be that she is saying out loud all the choices she is thinking about, or hasn't been able to settle on what character she is going to be, or just likes to change her mind a lot.
Instead of saying, "come here kitty" you could say, "Oh are you a kitty?" or "what are you now?" But I think just being quiet until she settles in to a role or asks you to do or be something would be easier for you.
I don't have any sort of education in child psychology, so I can't say for certain that this isn't an indicator of some problem, but I wouldn't worry myself unless she exhibits other worrisome signs or odd behaviors too. I would guess it is more likely just a phase. It's hard to know what is really going through a kid's mind. You don't sound like you are worried about it, but if you did become worried, you could always ask a pediatrician about it too.