Wikipedia does not list her death year. Also, I have never been able to find her exact birthdate (do NOT trust Goodreads when it comes to birthdates), but chances are she was not 87 yet.

She also wrote the sci-fi Ormingat trilogy.

https://www.librarything.com/author/waughsylvia
(with photo and exact death date)

From Goodreads:

Sylvia Waugh (sounds like "cough") was born in Gateshead, County Durham -there was no Tyne & Wear till 1974- in Northern England in 1935. Having worked full-time as a grammar teacher for seventeen years, Waugh began her writing career in her late forties, after her three children were grown. In 1993, she published her first book, The Mennyms, which eventually evolved into an entire series. Ms. Waugh said in an "Entertainment Weekly," interview with Lois Alter Mark, "I created the Mennyms because the world is too cynical, too lacking in magic. People with dreams are an endangered species, and I wanted to write for them. I don't want the nastiness-the stuff I see on TV.." Since completing her "Mennyms" books, Waugh has continued her focus, as "Horn Book" contributor Martha V. Parravano noted, on "what it means to be human by exploring the lives of those who are not."

https://www.fantasticfiction.com/w/sylvia-waugh/
(book covers)

https://www.kirkusreviews.com/author/sylvia-waugh/
(four Kirkus reviews)

https://www.goodreads.com/author/show/36112.Sylvia_Waugh

About "The Mennyms":

"A family of life-sized rag dolls live quietly and happily in a British village, secure that everyone takes them as human, until a letter from their landlord's relative in Australia threatens their existence."

https://en.wikipedia.org/wiki/Sylvia_Waugh

Excerpt:

Awards

Beside winning the Guardian Prize,[3] The Mennyms (book one) was recognised in other ways:

The Birmingham Readers & Writers Children's Book Award - a new prize, selected by schoolchildren[citation needed]
An official commendation and the Silver Kiss (CPNB) for the Dutch 'Mennyms under Siege'[citation needed]
A certificate from the American Hungry Mind Review naming it one of its 'Children's Books of Distinction'[citation needed]
American Parenting magazine's 'Reading Magic Awards' - one of the top ten children's books in the USA for 1994, and one of the ten books of the decade that 'best withstand the test of time'.[citation needed]
The whole series was awarded the Kinderbuchpreis 2000 in Vienna.[citation needed]

https://www.google.com/search?sca_esv=601262482&q=%22sylvia+waugh%22&tbm=vid&source=lnms&sa=X&ved=2ahUKEwiZ0qHcsveDAxVmCnkGHQooAtwQ0pQJegQIDBAB&biw=1920&bih=925&dpr=1
(two videos about her books)

https://groups.google.com/g/rec.arts.sf.written/c/77YeSxC0C7w/m/5Z2ifF_NBQAJ
(birthday post from 2015)