Lost one of my mice today, Delilah. I had 5 pets, 2 cats and three mice. I had planned on 2 mice, however was mistakenly given a male and female. The females become depressed and upset when they're alone. So Enter Delilah the therapy mouse. We tried to house Lily alone for a bit. She became aggressive and depressed. She barely ate if at all, hissed and nipped which she'd never done before. We introduced Delilah, a bright orange girl and within a week If say Lily recovered. They were sweet together but very different.
I'm not super hands on with mouse as pets. They don't enjoy being picked up. But occasionally I would. They are more of a spectator pet. You care for them, give them the things they need but they take care of their own house. They build and interact and are a snapshot of life in a vessel.
This particular sweet little rodent was gentle and very inquisitive. She wasn't afraid of much. Most importantly she was everything Lily needed her to be.
She died in her sleep. She looked comfortable. I wish the critter the best in her next life.