Introducing two female mice?

[Mia]

So. You've probably seen all of my mouse questions because I have had serious problems with my three females... Cloud, Moo, and Rescue. I bought them a month ago and Cloud bites Moo nonstop and now Rescue has started. She is definitely the bottom in the mousey-pack. Pet Emporium and PetsMart both said to separate them before they kill her, so I did. At first I wanted to put in a cage divide (oh, I have a ten gal tank) so whoever is separated can interact through bars or plastic. They said that a mouse would chew through it just to kill of the mouse on the other side so she has the best chance of mating (yeah, not gonna happen sweetie. ) and stuff.
As a back-up plan (since females may become depressed when alone) I will buy another female for her. Can I have the steps for introducing, as well as risks and possible ways to prevent them? I know it's risky, but if it comes to it I will do whatever it takes. I know she's just a mouse, but she is a living creature and no living thing should die of loneliness and depression. I need to introduce as fast as I can because I have no other cages and I don't need another one! I could introduce in a neutral environment and keep them there for a few hours and watch them and then scrub the cage clean so there is no scents. They would be about a month or two apart in age, so I don't think that will be a difference.

Please help, I will choose the best answer ASAP