Why does Raven hate her birthday?

Why Raven Dislikes Her Birthday

During the conversation, Raven offers some insight into her feelings. She mentions that at the time of her birth, a group (likely the priests of Azarath, although the specifics are not provided) looked into her future and foresaw that something dreadful was destined to occur on this day. This grim vision is the reason she refrains from celebrating.