She began her professional career in France, with Stade de Reims, then settled in Italy where she found success with Serie A teams including Lazio and Trani.
After qualifying as a coach at the Coverciano centre, O'Brien worked for the Italian Football Federation (FIGC) and served Lazio as manager.
O'Brien enjoyed similar success in Italy, collecting six Scudetti and two Italian Women's Cups in a career spanning seven clubs and 18 years.
[2] The Dizionario del Calcio Italiano described O'Brien as an elegant midfield playmaker, adept at reading the game and capable of precise passing.
[4] O'Brien told Newstalk radio in August 2014 that she won about four caps but was never invited to play for Ireland while based in continental Europe.