Turns out that at least six of her novels were juveniles, mainly about teens with disabilities.
An Open Mind, 1978.
"Torn by conflicting loyalties and emotions, a teen-age boy finally comes to terms with his father's pending remarriage with the help of a spastic boy." (The latter boy, Bruce, has cerebral palsy.)
A Time for Everything, 1979
"A young girl grows up amid many family problems in a small English village during World War II."
Only Love, 1980.
"When she finds herself the object of a young man's love, a spirited, physically handicapped 16-year-old is both touched and frightened for she knows she may now have to share her painful secret."
Sweet Frannie, 1981
"Paralysed from the waist down and confined to a wheelchair, Fran realises she hasn’t much of a future, but when she goes into Thornton Hall Residential Home, things begin to look up. For a start, she has a room of her own for the first time in her life. And pretty soon there’s someone else to think about: eighteen-year-old Luke Hawkins. After all, who better than fiercely independent Fran to help a young boy who has just lost both his legs in a road accident? A book of sweet and sour emotions that will bring tears of admiration and amusement as well as sadness."
Secret Places of the Stairs, 1984
"Seventeen-year-old Cass misunderstands her divorced parents until she discovers the secret they've been keeping from her: she has a severely handicapped, terminally ill younger sister."
No Time at All, 1994.
"Two disabled children love their new bungalow by the sea. It even has its own spectral steam-train which only they can hear each night. The train holds many mysteries which will change their lives."
From 2004, by Lois Keith:
"What Writers Did Next: Disability, Illness and Cure in books in the Second Half of the 20th Century"
The article refers to Sallis' books, plus Jane Eyre, Little Women, Heidi, The Secret Garden, What Katy Did, Deenie (by Judy Blume), and Izzy Willy-Nilly (by Cynthia Voigt).