Thayer is an average honey blonde girl with brown eyes. Her nose is slightly upturned and has a smattering of freckles across her cheeks and nose. She has a slight tan from traveling with her family to Greece during the summer.

Thayer is an outgoing girl who is slow to trust. Her parents were both Slytherins and her twin brothers were both Slytherin and Ravenclaw, so she is used to not showing her weaknesses. She enjoys riding brooms and reading outside.

Thayer enjoys spending time with her parents and her twin older brothers. Although pure-blooded, they live in a comfortable house in Scotland. Her twin older brothers are Lyle and Everett who are 2 years older than her. They often are found flying on brooms on their property and riding their Abraxans. Her father, Charles, is an Auror and their mother is a Potioneer for a large company. She has several friends that were made from her parents friends children and from siblings of her brothers friends. Her parents often have large gatherings at their house to spend time with their friends, which allows Thayer to meet new people.

The first time she had a burst of accidental magic was when she was fighting with her brothers when she was 5. In the middle of a tussle between Lyle and Everett, she managed to turn Lyle's hair green and blasted Everett's eyebrows off. Although Lyle and Everett were not pleased to have unwanted changes to their body, they screamed with delight and ran to tell their parents.