When meeting her victims in person, she would wear baggy tracksuit bottoms and a hoodie, and would tie her hair up in a bun and hide it under a baseball cap.
The fake persona was so convincing, she even spent extended time with some of her victim's parents.
When one of her victims, a 14-year-old girl, asked her about her breasts, she claimed they were "man boobs" she had grown when she was overweight. When the same girl found pictures of Watts dressed as a woman, Watts convinced her she was just experimenting with wearing girls' clothing.
Watts even stuffed her pants with rolled up socks to trick her into thinking she had a penis.
The court heard Watts became increasingly violent towards the girl, trying to push her into the path of a vehicle, and threatening her with a knife.
When she was finally arrested, she told police she considered her sexual exploits a game, and claimed: "I was only trying to cheer them up."
Judge Susan Evans said Watts targeted victims with low-self esteem or who had been bullied; after learning the truth, some of her victims self harmed or even attempted suicide.
In a victim impact statement, the 14-year-old admitted she had been in love with "Jake" and thought she could tell him anything, and that her "heart exploded" when she discovered the truth. "She's in my head," she said. "What she has done to me is gross, horrible."
Another 14-year-old victim told the court about how excited she had been sharing her first ever "proper kiss" with a boy.
Watts pled guilty to seven offenses involving four girls: one assault by penetration, three sexual assaults, and three counts of meeting a child following sexual grooming.
However investigators believe she had many more victims, who may only now realize they fell prey to her, and appealed for them to come forward.
"I think there will be further victims, who were in a relationship with Watts, who will now realize she is a woman," officer Phillipa Kenwright of the Metropolitan Police said. "I think there could be 20 to 50."