The 30-year-old, who starred in the second series of the BAFTA-winning ITV2 reality show, has been on a heavy fitness regime since April, according to Heat.
"Gemma's been working really hard… she's been extremely focused on getting into shape and she's looking amazing," a source told the magazine.
"It's helped her confidence as well - she's ready to hold her own against Lauren, Sam and Chloe in the new shows," the insider added.
Previously, the star had said that she felt "sexy" at 17 stone, and insisted that she was not looking to lose weight.
Collins was left heartbroken in TOWIE's series two finale after being snubbed by Mick Norcross, but the pair have since made up.