Siobhan made 27 appearances during her United career.
Everyone at the club would like to thank Siobhan for her service and wish her well for the future.
Casey Stoney said:
“I want to thank Siobhan for her time with us. Aside from her obvious goalkeeping abilities, she has been an incredible leader and role model within the team, and a fantastic mentor to the talented young goalkeepers we have at United.