Do you have a Habit Trail? It' he plastic cage that connects rooms through tubes. This is a great way for her to have her own room away from the male. As she starts gestating, she will begin to nest (gathering items and making a secluded area); her stomach will also begin to get bigger. She won't be as active as before. She'll also appear tired.

 You can tell if your hamster is pregnant because it will sleep a lot more and will make a little bed in the corner and it will want a lot more attention and eat more than normal..and you should hold it more often and give it clean bedding more often and give it a bit more food than normal and a couple of days before it gives birth give the cage a really good clean because you won't be able to clean the cage for a while to find more information go on