The website from which this image is taken explains that mice are christian symbols for souls in Purgatory, and this may explain it. Mice do not appear to have a patron saint of their own, but my research consists only of several search engines' first page results.
By James C. Christensen
Other images, such as the one on the left, do surround her with the furry ones themselves. Good night, all. I shall be setting up a small suitable shrine for Saint Gertrude, or thumbing through my Sylvia books and imagining what one might look like from my non-traditional and quasi-polytheistic approach religion and the numinous. But go and read "A Band of Feline Brothers."