It's left out on that page as this wiki is still a growing resource and many pages do not have enough information as they should due to an inactive userbase.
Well, Narnia is a modern version of creatures from mythology and fantasy. It doesn't follow traditional mythological depictions. The faun is not portrayed as erotic in Narnia like in the Ancient Greek/Roman mythology. So no, the little girl is not the nymph of him. Additionally, she is a human and not a nymph because nymphs are divine deities. They're similar to goddesses but have many differences between them. As far as I know, the little girl doesn't exhibit any of these qualities.