It appears Donovan and Masters have been roommates all during medical school and remain roommates entering their internships. Donovan appears to think that Masters is too high strung, and often tells her to relax her study habits. Unlike some of Masters' other classmates, Donovan won't make fun of Masters or make jokes at her expense, but she realizes Masters appreciates people being honest with her and doesn't hesitate to reveal to Masters that her behavior is "weird", although harmless.
Donovan was the first person to tell Masters that Gregory House has posted an opening for an intern and realized before Masters did that House wasn't looking for anyone other than Masters. Donovan encouraged Masters to take the opportunity because Masters gets on most people's nerves with her honesty and forthwrightness, but House wasn't bothered by it.