My sister has been crying hysterically every since her fiance died 6 months ago. isnt it time to let go?

She's hurting. Don't judge her for that. She loved this guy with every fiber of her being and he was taken from her. She needs more than 6 months to learn how to deal with the situation, but she may never get over it. Suggest talking to a psychologist, it's the best you can do.