Stops after braking downhill

Hello, Newcomer needs help for my 80 year old aunt. She has an 89 escort that only has 60,000 miles on it. Problem being is when whe goes down a steep hill after applying the brakes to stop the engine dies. The car will restart immediately. My cousin told her the gas cap wasn't on tight. She filled the car with fresh gas and made sure the cap is on tight. It hasn't stopped on her again we are just afraid to trust it. Any help with this would be appreciated. Thanks