I give below a dialogue in which your question and answer are possible. However, note that the question is not asking about a person's job
Three people are round the bed of a man, Bill, in a hospital room. Ben, an old friend o Bill comes into the room. He greets Sam, Bill's son:
Ben: Hi Sam.
Sam. Hi. Ben. (Indicating the other two people round the bed) Do you know Mary and Jill?
Ben: Yes, I do. Hi. (indicating a person in the corner of the room) Who's she?
Sam: Oh, She's a doctor.
[My invented dialogue would be more natural with she would be more natural with that, but my point is that it's possible as it is.]