Lewin was Arsenal’s first-team physio for 22 years and also worked as England’s head physiotherapist between 2008 and 2016.
The 52-year-old will now link up with Pedro Martinez Losa’s squad as cover for Mary Shiels, who is on maternity leave.
Gary said: “It's a pleasure to join the team at Arsenal Ladies and see how much the women's game has come on since I was here with the men’s team from 1986 until 2008.
“With the upcoming SSE Women’s FA Cup rounds and the Spring Series, it's a very exciting time to be part of this club.”
Arsenal Ladies began their new season in style on Sunday, the FA Cup holders beginning their defence with a crushing 10-0 win over North London rivals Tottenham at Meadow Park.
Danielle van de Donk scored a hat-trick and Danielle Carter netted two for the holders, who will face Birmingham City in the last eight.