On her way back to the campus, she met Heather, and approached her. They began chatting, until, eventually, Heather took Bill to look at a strange puddle in a lot nearby.
Later, the Doctor ran across the courtyard, with Bill after him, to check out that puddle. That evening, that same sentient puddle, taking the form of Heather, confronted Bill outside the university building, having chased Bill from her flat. She immediately ran up to the Doctor's study. (TV: The Pilot)