When will my mouse give birth?

I recently bought a mouse from the pet store. I bought her about a week ago because they told me she was preggo. And since i breed my mice for my snakes a preggo mouse for 2 buck is worth it. When i got her she looked like she was going to pop that night. But it has been a week and she hasn't gained any weight but i can feel the babies in her. She weighs around 91 grams. I know she isn't just fat because her stomach is big but her upper body is slim. She is a brown mouse. I bought it mainly because of the color. I really wanted to get more color into my mice besides white. Could i put one or two pinkies i have in with her to try and induce birth. Thanks for any help.