Since posting about the incident on social media, it has been shared more than 8000 times. Mcewen also informed police and the SPCA.
Mcewen said the entire experience was "awful" and nothing she ever wished to see again.
"I was so upset, I have animals of my own and I'd never wish them any harm."
A police spokeswoman on Thursday night said they had spoken to all those involved and "based on the information available at this time, police do not believe the cat was thrown out a car window, although it may have appeared this way to some witnesses".
She said the SPCA Inspector will continue to try to locate the cat. However, should "additional information come to light, it will be assessed".