New mouse not happy, very worried

Well, I'm not a mouse expert, but I would seperate them for a day or two, see if she improves. They will fight and get into a new order sometimes. Some mice won't eat or drink with humans (or threats in their minds if they aren't socialized) near them. Just let her relax, seperate them if you have to, and let them feel the idea of loneliness again.

Is her breathing obvious and very rapid? Is there any crackling noises when she breathes? And how quickly did the mouse develop this? When you say hunched, do you mean her back is arched and will not relax? And does her face look skinny and stomach look hollow?

Pardon all the questions, but if what I decribed above is symptoms she is showing this is serious, and you need to move her out and away from your other doe now.
If you are willing to take her to the vets, do it quickly.

I have had a mouse that showed the symptoms I described above (though the crackly breathing appeared towards the end), I'm not entiredly definate on what it was, but I think it was lower respitory disease or pnuemonia.

Though I may have got the wrong idea when you said hunched... hehe Better to be safe than sorry I say.

Willow xx

Thanks for all your posts. Sadly she died in the night. Her breathing had been very obvious, and we were going to take her to the vet today. We'll know better next time.

Keep a close eye on your other doe, lower resp problems aren't generally as contagious as other stuff, but like I said above, always better to be safe than sorry.

Willow xx