Hey gyn nurses....help me out here please

My mother had a TVH a few months ago. She went for a pap smear???? why is that first of all....secondly, they said they found some white cells so she needs to be checked again. Why pap smear when everything is gone? What do white cells usually indicate? I don't understand, because I thought there was nothing there to pap smear, ya know? I am an SICU nurse who never deals with gyn issues. I appreciate your input on this....