What Causes My Granny to See Things That Aren't There?

My granny had mice a couple months back. My husband mowed the field with the tractor & i think they all ran toward the house after that but we caught mayb 15 mice in traps within a months time and got them pretty much under control. The past few weeks granny has been telling us she has been up all night fighting mice. She says she hears the babies crying and sees the mama daddy and the babies running all over her bathroom. We set traps everywhere in her bathroom and we havent seen any sign of mice. None on traps or no droppings! She told us their running under the wallpaper and under the carpet. Well my husband decided to spent the night and sit up and listen out for them. He didnt hear or see a single thing! I went back to her bathroom the other day and she was standing in doorway looking at the floor and i said granny do u hear them or see them. She said" yes u dont hear them, their making an awful noise" and i didnt hear a thing and she pointed at the floor and said "look their they are shes having babies" I got on my knees closer to the floor and she did the same and she had a hammer and she said " look here they all come "and she was wacking at the floor with the hammer like she was trying to hit them! There was absolutely nothing there. She is still constantly hearing and seeing them and losing sleep every night but there are no more mice in her house and havent been since we caught the 15. We had a pest control come out and he even told her they were under control and if they were there they would have gotten on trap by now. How is she seeing these things that are not there and hearing things that are not there? please help cuz its freaking us out and we are very worried about her!!! Thanks