Years ago in elementary school, I read a young adult's fantasy novel. The story was about a young girl training to be a sacred priestess of some kind with a monk (?) in a holy sacred caverns that had to be kept dark. She and the monk who I think was blind were the only ones allowed in. There were some books or relics in the caverns. She was either blindfolded or in complete darkness for some time. The main characters were the young woman and the (blind?) monk attending her.
I want to say the cave was part of a monastery or some religious building. Eventually, her training is interrupted, and they catch someone in the caves, or she is 'rescued' from the caves.
The majority of the first chapters of the book went into detail about her training, being in the dark in the caves, and the monk who followed her. She may or may not have been an orphan but the idea was a priestess of this sacred cave was trained from childhood to become 'the' priestess of it and keeper of the relics in it I suppose.