Reddit reviews Descent Into Madness

I'm seeing Angelhead: My Brother's Descent into Madness, January First: A Child's Descent into Madness and Her Father's Struggle to Save Her, Descent into Madness: A Personal Look into Schizophrenia, and The Center Cannot Hold: My Journey Through Madness. All of those are about schizophrenia, none of them are textbooks or as old as you describe.

Not every older book is possible to find with google. It's possible that she has the title exactly right, and it's just so obscure that nobody is talking about it online.

Inter-Library Loan is a great way to get ahold of rare books. If you have enough information, you can give that information to the library, and they'll check with other libraries until they find one that has the book. Then that library mails the book to your library. It can cost some money, but sometimes it's the only way to find some rare books.