Cat pregnancy worries

Ive been given this 10 month old cat from a friend to babysit for 2 months. She told me there was a chance she waz pregnant and just recently she's been starting to show so im pretty sure she is. Ive calculated the cat is due to give birth around the same time the owner is ready to take her home. Im just worried that a change in environment so close to (or even after) giving birth might cause the cat to stress and reject her kittens. If that is a possibility what would be the best thing to do. I also have worries about her haveing kittens so young, shez only a kitten herself compared to my two cats.