Mabel Hubbard Bell supported her husband in pretty much all of his work, even the eugenics.

Mabel was born hearing and became deaf from illness at a young age, prompting her father to found the Clarke School for the Deaf, an oralist school. She took speech classes into adulthood, including from Alexander Graham Bell, which is how they met. She was considered one of the best lipreaders of her time and prided herself on passing for hearing as much as possible.

AGB's eugenicist views said that people with congenital deafness shouldn't get married to each other, because deafness was an affliction and a problem. Because Mabel became deaf later in life, eugenics wouldn't apply to her; she supported the idea of deaf people being as close to hearing as possible and agreed that they should not marry.

Source: Katie Booth's The Invention of Miracles