Mrs.Smith is Logan Wilde's pet mouse along with Mr. Smith and the other pets that Logan owns during the course of the Menagerie Trilogy. Squorp called the mice "small scritchies", and wanted to eat them. He did end up eating their food. But luckily, Logan talked Squorp out of eating the mice.
Mrs. Smith lives in a terrarium with Mr. Smith that sits on Logan's desk. Logan noted that it was odd that Purrsimon, his cat, was not watching him feed the mice, as this appeared to be one of her favorite pass-times.