What is the first name of Donald Duck's twin sister?

Thelma "Della" Duck is a cartoon character and core member of the Disney Duck family, both as the twin sister of Donald Duck and the mother of Donald's famous nephews Huey, Dewey, and Louie. Della is an anthropomorphic white duck with a yellow-orange bill, legs, and feet. She typically wears an aviator hat, bomber jacket, pants, and as an adult, a robotic prosthetic leg. Della is famous for her less temperamental personality and adventurous spirit, and as a female adventurer and an amputee, for being a positive role model to young girls and to children with disabilities.

Della Duck was first mentioned in "Donald Duck" comic strips and animated short films in the late 1930s. However, prior to her animation debut in the 2017 "DuckTales" reboot, Della never appeared in any animated film or television series, and had only limited appearances in Disney comics. As a result, not much was known about the character prior to 2017.