"How would your mother describe you?"
You can use more personal words here because your mother knows you in a different way.
"I think my mother would say I'm very friendly because I had a lot of friends and that I'm very focused because I always finish what I start."
This answer is showing two different types of characteristics. One is more personal and one is a good work trait. It also shows reasons by saying because... Overall, these types of questions are not that significant and a short answer that is good should be fine.
"Since I was the oldest out of three, I think my mother would describe me as responsible and someone who is looked to for answers."
"My mother told me I was always smart. When I was younger, she was surprised to see A's in my report card. After awhile, she would be surprised when I didn't receive an A."