- You may be looking for Mrs Ali.
Ali was a college student. Over the course of her education she learned in science that TARDISes were theoretically possible and in ancient history she was told that Time Lords were extinct. Although she considered technology "ridiculously retro", she was proficient in using it.
The Doctor and Ali defeated the Starman, and the Doctor took her back home to Karkinos. Although Ali had saved his life and in fact had helped save the day, the fact she allowed herself to go into a battle rage and mercilessly kill a number of Babylonian soldiers made him uneasy, and he indicated he would not take her on as a companion.