introducing girl mice

Question
I've had my mouse (named Baby) for about 20 months, so shes getting quite old. She is still active though and a great pet. A few days ago I decided to buy another mouse for her to have as a friend and so that I won't be upset when Baby dies.
I have Baby and the new mouse in separate cages next to each other so they can get used to each other. However, I'm not sure how to introduce them. The old mouse, Baby, seems very interested, and keeps looking over and sniffing the air.
The new one is very jumpy though (quite literally) and nearly escaped when I tried putting her in her cage. She seems to be very nervous and is always either hiding or running on her wheel.
Do you think the new mouse will calm down after a while in order for me to be able to handle her and introduce her to Baby, or should I just put Baby into the cage with the new younger mouse? Please let me know if I've done anything wrong.
I've asked you a question before and it was very helpful, so thank you.

Answer
Dear Joy,

Put Baby and the new mouse together in a clean cage with clean toys.  Take a dab of REAL vanilla essence and dab their butts and chins, so they smell the same.  Expect some chasing and squeaking, but as long as there is no blood, they sleep together, and both are relatively active, things are going well.  

Have fun : )

squeaks n giggles,

Natasha