other females in cage with pregnant mouse?

Question
I bought 4 female mice from a pet store a week ago and in the past couple of days one of my new girls has been looking noticeably rounder than her sisters. She is rather pear shaped with bulges on either side of her belly, so I think she will be having baby mice on the way! I have checked the 3 other girls and confirmed that they are in fact girls. The somewhat funny thing about this is that I got these mice from a small pet store that separates its male and female mice, so I didn't think that this would be a problem! Fortunately the female (Bree) who looks pregnant is one of the two who are more friendly and willing to be handled.

My question is should I separate Bree from her sisters and put her in a different cage so she can have privacy or should I leave her in the main cage with the other females? All 4 are young and so wouldn't have had litters before, and none of the others look pregnant.

Thanks in advance for your help!

Answer
Dear Angela,

Bree will be very happy to share nest-keeping responsibilities with her girlfriends.  That gives her more time to run  in the wheel and eat, without the babies getting cold.  Mice make very good aunts as they take care of each others' babies very nicely.

Because baby mice can precociously be ready to mate at age 4 1/2 weeks, it isn't so strange that a mistake was made in the timing of the separation of males and females.

Best of luck to Bree, and have fun with the babies!  There are a bunch of pregnant-mouse-baby-raising questions in my archives ("see past answers") if you look around.  Otherwise feel free to write back with any questions of your own.

squeaks n giggles,

Natasha