Several things come to mind of what she could be holding. 1 A item that will put saint on a higher tier/rank. (hopefully tier) 2 A locked box that goes to that key Sunless has. 3 A piece of history like a journal that only Sunless can read. 4 Something else that is important.
Great cliffhanger, painful. Oh and great chapter. Keep hoping that his inhuman echo will gain some degree of self awareness/sentience like his first shadow has