The National Crime Agency (NCA) said Christine Callaghan, 33, of Bexhill, was paid £2,285 by Dean Petley, 30, to carry out the abuse over Skype.
On Friday (November 8), Callaghan admitted four charges at Isleworth Crown Court.
Petley, an automotive engineer, admitted 11 charges last month and was jailed at the same hearing for eight years, the NCA said.
NCA officers discovered the duo’s offending through an investigation into Jodie Little, 30, who was jailed for 12 years and four months in August for sexually abusing children online, the agency said.
In July last year the NCA said it became aware of Little sexually abusing children under two unique online names on an adult services website from her home in northern Cyprus.
The NCA said she admitted nine offences and was convicted of eight using Section 72 of the Sexual Offences Act 2003, legislation designed to prosecute British nationals in the UK for crimes committed abroad.
The agency said the investigation into Little generated new leads.
In October last year Petley, of Leamington Spa, Warwickshire, was arrested after being identified as one of Little’s customers.
Online chat extracted from Little’s devices showed he had asked her to perform sex acts in front of young children and that he paid her £750 ovewr a period of more than a year to see her sexually abuse two victims, the NCA added.
Little, originally from Huddersfield, sent Petley 10 electronic files, one of which showed her sexually abusing a very young girl and talking graphically about the child being raped.
The NCA said he was rearrested in May this year after further evidence was found on an encrypted hard drive at his home.
It contained screenshots of conversations with Callaghan over two years and full facial images of her abusing the girl with a small window of Petley watching it, the agency added.
NCA officers discovered evidence of Callaghan discussing what she would do for money and of Petley instructing her how to abuse the victim.
The hard drive also contained a video almost 10 minutes long of Callaghan abusing the young girl.
Screenshots showed that on at least 10 different dates over three years she performed penetrative sexual activity in front of the victim and also sexually abused her.
Five indecent images of children were also found on the drive.
Callaghan will be sentenced at a date to be confirmed.
Jason Booth, NCA operations manager, said: “Petley’s and Callaghan’s convictions were only possible because of our determination to make Jodie Little face justice.
“Distance is not a barrier for the NCA in pursuing UK child sex offenders wherever they are. The investigation into Little has unravelled other leads that our policing partners are working on.
“These were horrendous crimes, but they’re an example of what the NCA is seeing more and more with increasingly worsening cyber-enabled child sexual offending.
“The NCA knows that the scale and severity of offending against children are worsening.
“We and UK police arrest around 500 child sex offenders a month and safeguard about 700 children a month.
“There is no greater priority for us than protecting children.”