Why are the boys so puzzled when they find Jose Angelico's family plot in the graveyard?

Raphael, Rat, and Gardo are extremely confused when they reach Jose Angelico's family plot in Navaro Graveyard because when they get there, they see a grave marked with Pia Dante's name. Pia Dante is Jose Angelico's daughter and the boys have been sure that she is still alive. With the revelation of her headstone, the boys have no idea what to do next.