This is the 8448th most frequent Russian word.
находящаяся
"Located" or "being" (feminine, singular, participle).
In this sentence, the word 'находящаяся' is a participle describing the book, indicating its physical location.
Книга, находящаяся на столе, принадлежит моему брату.
The book on the table belongs to my brother.
Here, 'находящаяся' is used to describe the woman by her current state of being in a specific place.
Женщина, находящаяся в комнате, чувствует себя нехорошо.
The woman in the room feels unwell.
The participle 'находящаяся' specifies the item by its placement or presence within the box.