Good Food for Weight Gain

I've recently acquired a very small runt mouse, and I want to try to get her to pack on some pounds(er, grams)... I figure she is still young, so she might get a little bigger, but not much. Regardless, I believe it would be good of me to try to get her a little heavier than she is. What are the healthiest foods that I could give her to try to encourage weight gain? Scrambled egg, puppy food?

Is there any other kind of special care that would be beneficial for a runt? I'm keeping a close eye on how rough her two larger roommates are with her. Three three of them are newly grouped off together, and I know they're hard at work figuring out what the pecking order is(of course whatever it winds up being, the runt will be at the bottom), so bickering is to be expected, but I don't want the little girl to get hurt. At what point does minor scuffling over a particular piece of food or sleeping space become something to be concerned about? She's very sweet, and I want to make sure she gets the special treatment that she needs.



Sorry, I guess I should have posted this in the Health or General forums. Feel free to move the thread to wherever is most appropriate.