This is the 12456th most frequent Turkish word.
hissettiklerini
"What they feel."
Hissettiklerini refers to the feelings she experienced, used here in a possesive and relative clause structure.
Onun hissettiklerini anlamaya çalıştık.
We tried to understand what she was feeling.
Hissettiklerini indicates the feelings that she did not want to share, functioning as the direct object.
Hissettiklerini herkesle paylaşmak istemedi.
She didn't want to share what she felt with everyone.
Hissettiklerini here signifies the feelings she conveyed, used as the object of the verb 'anlatmayı'.