The Enid Blyton Society

My wife's favourite story is, I believe, one of Enid's. But she cannot remember the title. Only that her Grandmother read it to her as a very young girl.

It concerns a Monkey in a bedroom. It's tail is about to drop off. A fairy comes to the window and is cold and needs to come in. The Monkey let's in the fairy with his last strength. He then takes off his tail and wraps it around the fairy to keep her warm. She goes back out into the night. The next day the monkey wakes up as new.

I want to buy her the book for her birthday. Does anyone know this tale?

It's not exactly as you described, but there is a story in a book called Rainy Day Stories by Enid Blyton called The Monkey's Tail and is about a playroom of toys including a Monkey and a pixie who pops in every night. One day he has a cold and has no coat or scarf to go home in, so the Monkey lends him his tail to use as a scarf! When the pixie returns it, it is all washed and clean. Could this possibly be the one you're looking for?