She was left on the doorstep of St. Mary-on-the-Marsh Asylum and would have soon perished in the surrounding woods or been sent to a foundling hospital were it not for an act of uncharacteristic goodwill from the head doctor's son, following which she was handed off to another patient with the instruction to raise her. Raised she was, and the doctor's son eventually inherited the asylum, taking an interest in her education with a view to 'curing' her deficiencies and exhibiting her as a model child and marvel of modern psychiatry.

However, the best laid plans of mice and men often go awry.

When Mouse isn't trying to train the asylum rats to do tricks, she can be found drawing, playing cards, or exploring the asylum with her trusty companion Elpant.

She does not, will not, and cannot speak. You cannot make her. It's one of the immutable facts of the universe.