The word "it" undoubtedly refers to her surroundings, wherever she was (library, classroom, dorm room, or ?)
She couldn't concentrate on her studies ...
In the first sentence, the pronoun "it" refers to the study that she was trying to concentrate on.
In the first sentence, the pronoun 'it' refers to the act of studying. The sentence implies that the person mentioned in the first part of the sentence cannot concentrate on their study because there is too much noise around them. So, 'it' refers to the activity of studying, which is being negatively impacted by the noise.
