An England youth international, Baggaley has represented her country at U-17, 19, 20 and 23 level, and recently won the Nordic U-23 Cup.
Baggaley, 20, joined Birmingham City in 2014 and has made 18 appearances for the Blues between the sticks to date.
On her move to the West Country, the young shot-stopper says she is excited about the prospect of working with manager Willie Kirk and goalkeeping coach Neil Moore.
She said: “When I heard the Vixens were interested in taking me on loan I didn’t hesitate to come down, look at the facilities and meet the coaching staff.
“My aim for this season is to play as much as I can and develop under a manager that values youth development, which is a massive draw of this club.
“Caitlin Leach and Aimee Watson are fantastic keepers and I am looking forward to us spurring each other on and bringing out the best in one another in the season ahead.”
Kirk said of his latest recruit: “The plan was always to bring in another goalkeeper for the 2017/18 WSL 1 season to add competition to that area. By bringing in Sophie we have certainly done that.
“She is an extremely hard-working goalkeeper, who is technically very good and has strong distribution. I am excited to see how far both Sophie and Caitlin can push each other.
“We also have young Aimee, who shall continue to work hard in training with the first team and carry on developing.”