Former clubs have included Everton, Liverpool and Charlton - where she played under current manager Boanas.
The pinnacle of her career came in 2005, making her debut appearance for England against Italy. A further eight caps followed, as Fletcher was also included in the Euro 2005 squad.
Fletcher met her new team mates at training on Thursday evening, as they prepared for a friendly against MK Dons on Sunday.
Source - watford.fawsl.com