The SnoozeShade,a buggy black out to fit all buggies, has been an instant hit and Cara's company, Really Simple Ideas, is in profit after less than a year. She's also in the running for a BusinessMum of the Year award.
Miss Sayer, 38, was an events manager before she had her daughter Holly, now two. She thought she had left her business life behind her – until inspiration struck in a coffee shop with friends.
'Our kids wouldn't go to sleep,' she said. 'We were all trying to cover the buggies. We were all doing the same thing and I thought, this is ridiculous.
'I said that someone should invent a buggy cover and my friends told me to stop whinging and do it myself. So I did.'
After buying fabric which blocked out light while letting air through, Miss Sayer got a patent and had a prototype made. She took it to a baby product show in London, where it was an instant hit.
She was approached by a buyer for children's retailer JoJo Maman Bébé, who requested 100, and Kiddicare and Mothercare also showed interest.
She took a risk and used her savings of £30,000 to pay for the first 10,000 covers to be made.
They now sell in outlets including Halfords, Boots, John Lewis, and Amazon, with a major supermarket in the UK also planning to stock them in 300 stores. Fans include TV presenter Denise Van Outen, who's said she raves about it to her friends.
The £19.99 cover, called SnoozeShade, can strap on to almost all buggies. It has inbuilt UPF50+ sun protection, and is cool on hot days. It also features a 'sneak-a-peek' zip opening at the front so parents can check on their sleeping child.
Miss Sayer, who lives with husband Lucien Gover, 44, in Surrey, said inspiration for the cover came in part from feeling that mothers should not be made housebound by their children's sleeping patterns. 'But I never thought something like this would happen,' she said.
Miss Sayer says she grabs any spare moment during the day to respond to hundreds of daily work emails from around the world. 'It has been difficult and very busy at times. But it's amazing how fast everything's happened. I do most of my work when Holly is asleep or at nursery. When my husband comes home from work he is on bedtime duty so I can work.'
Antonia Chitty, of the BusinessMums Conference, which presents the BusinessMum of the Year award, said Cara is a testament that mothers can make it in business while bringing up children.
'Mothers can sometimes see themselves as being stuck at home,' she said. 'But being at home can also be about taking the time to think up ideas – something creative and new.'