Kasia, the main character in Girl in the Window by Penny Joelson, has ME/CFS.
Notes: US publication is titled The Girl Who Wasn’t There.
From the publisher:
Nothing ever happens on Kasia’s street. And Kasia would know, because her illness makes her spend days stuck at home, watching the world from her bedroom window. So when she sees what looks like a kidnapping, she’s not sure whether she can believe her own eyes … There was a girl in the window opposite – did she see something too? But when Kasia goes to find her she is told the most shocking thing of all. There is no girl.
UK publisher: Egmont Books (August 2018)
US publisher: Sourcebooks Fire (November 2020)
Author represented by: Anne Clark of Anne Clark Literary Agency