Hello there,
For some reason in the show, Cadance seemed to really like Starswirl the Bearded (Three’s a crowd, S4, ep 11), enough to keep up with Twilight’s fascination for his legacy (and himself). Quite peculiar for a pony who used to be a pegasus in her early years, thus not having as strong of an interest for magic as a unicorn.
Which is why here, the very first book she tried to lift with her new magic was one about Starswirl. It didn’t end well, but don’t worry, it was obviously just a copy.
… Right?
At least it made enough of an impression on her to want to know more about the guy whom she burned a book. Turns out she ended up really liking his stuff.