- You may be looking for Joan's namesake from the original novel.
While at Farringham, John Smith fell in love with her. He showed her a journal in which he had written down his dreams, which were his adventures with Rose and Martha before he was human. After John Smith became the Tenth Doctor again, she asked him if he could change back into John. He said yes, but when she asked if he would he said no. When he asked her to join him as a companion, she dismissed the idea immediately, saying that John Smith was dead and the Doctor just looked like him. She then asked the Doctor, "If you hadn't decided to come here on a whim, would any of these people have died?" He looked at her without answering. She dismissed him and, after he left, broke down, clutching John's journal. (TV: Human Nature, The Family of Blood)
Many years later, Joan's diary was found by her great-granddaughter Verity Newman. Verity published A Journal of Impossible Things, the story of Joan's love story with the Doctor which Verity told people who bought the book. As his regeneration into the Eleventh Doctor approached, the Doctor bought Joan's book and asked Verity, who realised who he was, if Joan was happy in the end. Verity confirmed that Joan did live a happy life after the Doctor left, but the Doctor left without answering when Verity asked if he too had been happy. (TV: The End of Time)