From Become someone
Missy is working as a waitress at the Cock and bull during the night shift. Missy's house is located in the Residential district
To progress with Missy main quest You will need to raise her Trust. But to progress with Missy slave quest you will need to raise your Dominance and her Corruption.
When Missy is working at the Cock and bull, she will always be there, every day of the week (11am to 1pm). For the rest of the day, up until 11pm, she is in random locations. From 11pm every day she is in her house.