From this era, it is fairly common to find photographs of women and girls, in a uniform borrowed from a male relative or friend.
With the newly formed women's services, you will need to use judgement to decide if the sitter was a servicewoman or not.
It may be be obvious from the pose that it was taken for fun. Other clues are a very badly fitting uniform or long hair escaping from a cap. Girls often posed in pairs for a dare.
A common feature of this type of photo is the woman holding a cigarette, seen at the time as very masculine.
The Army Service Corps whose cap badge is shown here, had no women in its ranks but did control the Womens Forage Corps and worked alongside other Women's services.
I have seen group photographs with women in overalls wearing the ASC cap badge.
However in my opinion this is not a servicewoman.