Moonless cannot wear any equipment and is AI-controlled. Offering Rotten Meat in this situation will make Moonless get angry instead. In hardmode, it is impossible to recruit unique allies to your party. If you refuse to let Moonless join the party when offered, she will not appear again. She can be recruited as a party member by talking with her during battle and offering rotten meat twice. Moonless is a special encounter that can be found when descending into the cavern using the elevator from the blood pit.
So now she roams the caves alone, in search of food for herself and perhaps for a new pack whom she can call her own, wherever that may be. It might have been because of the black, and the madness and sickness it induces in all living creatures living within the areas under influence of the Dungeons of Fear and Hunger. However, she was driven away by them because of this same strength. Because of her superior strength, she might have been the matriarch of the group. Moonless is a cave wolf that used to be a part of a pack of other wolves like her. The black has its way of changing the nature of wolves.' - The New Gods when asked about Moonless. 'A lone cave wolf who was once driven away from her pack because of her superior strength.
