"Simon has worked hard at his recovery and told me he's walking 10,000 steps a day that's around five miles -- way more than he was before the accident. He's got one of those watches that measures every step," she said.
While he is still getting help from doctors, Sinitta said Cowell has also cut down on cigarettes. He is also getting support from his partner Lauren Silverman, with whom he has six-year-old son Eric.
"He's still having a lot of physiotherapy, seeing great doctors and doing nonweight bearing pool work especially for spinal injuries. Simon has really looked after himself. Lauren and his team have taken great care of him and he's being sensible," said Sinitta.
Simon has broken his back "in a number of places" after falling from the new bike he'd been testing in the courtyard of his Malibu home.
After the accident, Cowell had to cancel appearances on the show "Britain's Got Talent".
Sinitta said taking a break from work has helped him focus on his health and loved ones.