The sexual predator is unemployed and lived at home with her mother in Enfield, North London.
Winchester Crown Court heard how she would compliment the girls online and call them "babe", then ask for their numbers and shift the messaging to WhatsApp.
She was caught when a doctor told Hampshire Police about his worries over a girl in a sexual relationship with an older boy.
Many of the victims didn't realise they'd been tricked until they were told by police.
Watts has been jailed for eight years.
She pleaded guilty to assault by penetration, three counts of sexual assault, and two counts of meeting a child following sexual grooming in incidents involving four separate victims.