This is the 12084th most frequent Russian word.
избавившая
"Having freed" or "having rid (someone/something) of."
The word 'избавившей' acts as a relative participle describing the girl who performed the action of freeing in the past.
Она была девушкой, избавившей меня от сомнений.
She was the girl who freed me from doubts.
Here, 'избавившую' serves as a relative participle modifying 'судьбу,' providing a past action context.
Они благодарили судьбу, избавившую их от бед.
They thanked fate, which freed them from troubles.
In this instance, 'избавившая' describes the book as having performed a freeing action in the past.