You know you are coming up on this boss slightly after you encounter Carmella, a previous boss from LOS 1.
In her first phase she rolls around in a ball like object while summoning minions. The objective here is to whale in her as much as possible while having RB active to break the ball.
During this second phase she will teleport around the arena while summoning more minions. Target her with LB active and hit her with the ice RT move. She will remain frozen for a few hits; rinse and repeat.
Shortly after you gain the mist teleport ability and teleport through the cage to drink Marie’s blood. Once this is done continue the fight by any means and the fight should shortly be over. Good luck hunting.