Introducing pet mice

Question
I have had two does for about six months now (there were two more before but they are no longer with us due to aggression and injury).  The two mice I have seem to get along well, with only a little squabbling here and there.

Last night, I wandered into a Petland (which I know I shouldn't have done) and fell in love with a darling little doe.  They say she is pregnant (which is half the reason I got her) as she was in the enclosure with four bucks, but I won't be 100% sure until the last week or so of her pregnancy.  She is currently in her cage by herself.

My question to you is, after the newest mouse gives birth and weans her pups, how would I go about introducing my two older mice to her so they could all live in the same cage?  I know how social mice are and that it would be in her best interest to have her live with the others.  I have very briefly let both of my older mice "meet" her on neutral ground in a small container I put them in while I clean their cage and they just sniffed each other (both of the older mice were very persistent in sniffing the new mouse's genitals - does this mean anything regarding her probably pregnancy?).  My newest mouse is so little (probably only 8 weeks) that I'm a little afraid of just plopping her in with the others.

What are some ways I could introduce them enough so that they could live together?

-Dana, Xanthe, Calypso, and Rhea

Answer
Dear Dana etc,

If she doesn't look pregnant yet, she can be introduced to the others right away. Besides the fact that she is pretty lonely right now after losing all her friends, she will also appreciate the helping paws the other girls can give her raising the babies-- they will take turns sitting on the babies so she can run in the wheel and eat.

Clean out the whole cage and scrub everything that will go into the newly clean cage. Then a drop of REAL vanilla extract (not vanilla essence) on their chins and bums. Expect squeaking and chasing. That's fine. You may see the older ones mounting her; that is a show of dominance. You may see her turn around and stand up to present her belly to the others; she is saying "Don't hurt me, I'm only a baby" and the others should respect that.

The only reason to separate them is if there is blood; or if, after a day or two, she seems really depressed or they won't let her near the food or nest. There should be only one obvious place to sleep, to encourage them to sleep together.

Have fun with the babies!

squeaks n giggles,

Natasha