I would have to agree with Dand. Are you positively sure it was a female that died? I know its going to sound like a totally dumb question, but then again I've had petstore employees mis-sex rodents when I've wanted to purchase them. You'd think the presence of "danglies" from the rear would be a clue...but I guess some petstore employees must all be virgins or something.
I too have also noticed that the addition of another adult member into the colony will stop or delay production. A new male especially as the females are very ruthless to him. Females as well, because they have to establish a pecking order all over again and the new female is so timid after getting her arse beat every minute for a week, she may not cooperate when it comes to mating.
The BEST way I have found to add a female to an already established group is to save back big, healthy female offspring that you just never feed off. Or in my case to try to prevent as much inbreeding as I can, I'll steal a nice 'n healthy female that I like the looks of from another colony. However the key is to get one that's still nursing slightly. I don't know if its the milk breath or what, but if it smells like its been nursing the adult females don't attack it and instead adopt it as one of their own.
However in your case, you should have someone look pregnant by now. I'd say either yer male was the one that died, or he's now sterile...and I'd invest in another colony. I just never saw the trouble some people seem to have with mice. If you obey the "rules" ya can't go wrong, at least here. I just stick them together, they'll have a tussle now and then, and voila..babies.
:-offtopic
Oh, and RIP to Fuzzy. He died over last weekend. One of my original males that I purchased at Petsmart, over 3 years ago. Towards the end he had lost his fertility, but he never stopped trying! He was paired with a son of his for the longest time, but when he became annoyed with the babies climbing all over him, he went to live out the rest of his life with a pair of my rats, whom he adored.
Here's a pic of him enjoying his favourite past-time, chewing holes in the tubs of my mouse rack. He'd chew it, just so he could peek out I think. I never saw him escape once in the months that he did it.
He made the biggest, healthiest babies I've ever had. :cheers: to Fuzzy!