This is the 3147th most frequent Russian word.
лучшей
"Лучшей" means "the best" (feminine form).
The word "лучшей" is used in the instrumental singular feminine form and describes "она" being 'the best' in her career.
Она хочет стать лучшей в своей профессии.
She wants to become the best in her profession.
Here, "лучших" appears in the genitive plural form, indicating comparison or categorization related to books in literature.
Эта книга считается одной из лучших в литературе.
This book is considered one of the best in literature.
The word "лучшей" is instrumental singular feminine, complementing "версией," to convey self-improvement in a comparative sense.