Mousemuse being an old friend for Dogday and Catnap.
She was the one who calmed the group down after Dogday had gone missing, and said that Catnap might be right, and the Prototype might actually be their savior. Afterward, that was the factor why she'd survived - Catnap spared her, thanking for her help in " searching out the heretics".
She's blind in one eye, bearing a scar that was left by whom unknown - by Catnap or by Prototype. God-touched, as it were... ahem!
She blames her self for the death of the other smiling critters, hopeless to ever see anyone alive. Which is why Dogday was forced to give her a forceful hug when they met, to proof that he weren't another illusion from the red smoke.
Then she became convinced of the reality of the situation she was experiencing and couldn't believe her happiness at hugging the one she thought was dead.
Catnap and Dogday being the only ones she has left.
She wouldn't live through either of them death