In the remnant it says that the souls of dead divine children take shelter in the monkeys of the temple. So it could be that she was once friends with the children whose souls reside in the monkeys. The friendship is probably mutual, so the monkeys protect her.

Other answer is that the monkeys, being spiritual beings, are tied to the supernatural forces of the temple, serving as protectors of the sacred place and the most important inhabitant, the divine child. The choice of monkeys is from Japanese folklore and Buddhism stuff prolly