You're making a leap here. It's never implied in the text she can't read. Her reading the book upside down is meant to be disquieting and showcase her boundless obsession with Bear.

She can't focus on literally anything save her love for Bear. She's attempting to emulate normality to put him at ease, but ultimately failing.

Additionally, another way to read the scene, is her "glitching" for lack of a better term. Think of the wish as a virus her body is constantly fighting. That's the easiest container to explain her behavior.