Basically what @ConstantErasing said. I must emphasise that aggression can not be overstated. Use the rally mechanic when you get hit and cripple her limbs. When she tries to heal keep hitting to stagger. Also if you took the threaded cane the whip form does bonus damage to beast type enemies. If you took the Saw Cleaver as most people are want to do, then its default form does bonus damage to her. Also make use of power attacks to help break limbs.