The singer and actress gained 70lbs during her recent pregnancy with daughter Maxwell, and has not yet lost the extra weight.
Now, her mother Tina is among a number of people who have agreed to support Jessica on her weight-loss programme.
"Jessica's mum Tina Simpson is doing Weight Watchers, her assistant is doing it, people that work for her fashion company are doing it - Jess has enlisted everyone around her to try and lose weight," a source told RadarOnline
Jessica previously signed a $4 million spokesperson deal with Weight Watchers and will stick to their diet plans and advice along with her mother and friends.
Before committing to her new healthy regime, Jessica allegedly had a final "pig out" on her birthday last month.
"All of the fried and unhealthy food was eaten by Jess for the last time," the insider added. "She is so serious now about losing the weight by eating healthy."