She`s Jons mother, who makes alot of food (Garfield likes her). Lives in a farm with Jons father and brother. She sometimes sends Garfield sweaters she made herself, which Garfield does not like at all.
A curious thing is, that she was born in June 31st in the year 1940. June has 30 days. It might be that in Garfields universe, June has more days.