This is the 810th most frequent Russian word.
оказалась
"Turned out" or "found herself/himself/itself."
Here, 'оказались' is used to signify verification or proof of something being accurate or true.
Они оказались правы в своих предположениях.
They turned out to be correct in their assumptions.
This usage of 'оказалась' implies that she unexpectedly or coincidentally ended up being at home at that moment.
Она оказалась дома, когда начался дождь.
She found herself at home when the rain started.
In this sentence, 'оказалась' is used to indicate the realization or discovery of the book's characteristic after some experience.