How To Stop Our African Grey Parrot From Biting?

We have a 15 year old female African Parrot who is aggressively biting my dad and bringing blood. She belonged to my mom who the parrot loved and listened to and would never leave her side. My mom ped away 2 weeks ago and her behavior towards him has gotten very bad. He is trying everything he can think of but is almost at the point of getting rid of her. He wants to know if there is something he can be doing to calm her and gain her trust now that her *favorite* family member is gone. She will not attack me as much but will try to from time to time. She will also hide under the bed and wait for my kids and father to come by and lunge at their feet. She has bitten them several times this way as well. Please help if you can, so we can keep a part of something my mom loved very much.