Matt Sale's mother is an unseen character in Season 1 of Fear the Walking Dead.
Not much is known about Matt's mother before the outbreak, except that he lived in Los Angeles, where she married and became a mother.
During the outbreak, Matt's mother, as well as his father were on vacation. Some time after Matt Sale came down with the infection, both his parents returned home. It is implied, but never shown, that an infected Matt attacked them when they entered the Sale home, as the front door is seen left open and their bags are left in the car.