The ex-Sunderland, Leeds and Arsenal defender wrote on her personal website: "There is no easy way to say it, but I am retiring from football at the end of the current WSL season.
"Taking the decision to retire, is such a difficult thing to do. Whilst age comes to every player, it makes it no easier having to say the words out loud. Football has been my life; my passion and I have loved the career I have had."
She explained to City's website: "From a mental point of view, for me I am looking forward to a new challenge and I’m a little tired now. It’s been a heavy few years. I just feel as though [it’s the right time]. I’ve had a lot of discussions with my family, my agent and friends. I just needed to come out and say it and I feel now is the right time. I feel as though I’m ready to learn something new, whatever that might be. I’m grateful for the journey I’ve been on. At the same time, my body’s fine, but for me there are other things I want to be doing and spending more time with my family as well."