My condolences for your mouse that passed away, I am so sorry. 
I too have heard that female mice especially need to have female roomates to socialize with, but if you think your lone female seems happier alone, maybe she is just one of those mice that prefers to be alone? I am sure some mouse veterans on this forum will offer some good advice. It is a good question to bring up! Again, I am sorry for your other mouse.
I too have heard that female mice especially need to have female roomates to socialize with, but if you think your lone female seems happier alone, maybe she is just one of those mice that prefers to be alone? I am sure some mouse veterans on this forum will offer some good advice. It is a good question to bring up! Again, I am sorry for your other mouse.