Introducing a new mouse

Question
I have 2 young female mice I purchased from Petco 3 months ago.  One of the mice escaped 2 weeks ago and was killed by a cat.
So, I got another female mouse so Patchy wouldn't be so lonely.  However, when I introducted them today, Patchy immediately began to attack the new mouse.  The mice live in a 4 cage complex so there is enough territorial space.  I seperated one of the cages out for the new mouse - Pirate Girl - but would like them to live together.  
How can I introduce them and limit attacks?  Can I put Pirate girl in the biggest cage in a ball and let Patchy grow used to her that way?  Simply have them near each other in seperate cages or several days?

Answer
Hi Kristina,

I'm sorry to hear about your loss.  :(  Mice can be real escape artists.

Putting the cages near each other is a really great idea, but I'm not sure about the ball thing.  Those balls can really only be used for a short period of time, and since they distort how things look (like looking through a coke bottle) it probably wouldn't do much good.  Mice are big on smells, so you can try switching bedding between their two cages for a bit so that Patchy gets used to Pirate Girl's scent (cute names, by the way!).  I've only had two female mice in my whole life who couldn't be made to get along with anyone else (thank goodness they got along with each other!), so I would be very surprised if they didn't come around eventually.  Usually it just takes a couple of days of tussling to get the new social order decided upon.  Also, next time you try to introduce them you could try it in Pirate Girl's cage so Patchy feels a little less threatened.

One last thing you can try is putting them together and then giving them both a treat.  They'll be so happy about the treats that it could stave off fighting for a little while.

Best of luck, and I hope they figure each other out!
-Tam