Is it normal i fear the walking dead?

My grandmother has a collapsed face and dirty brownish teeth. Her set of teeth isn't complete anymore. Between most of them, there are tooth spaces filled with moldy food debris. She doesn't talk and my parents keep her inside her room. But they never lock her room and at night she often leaves her room and roams through the house. It gives me the creeps already but something else did even worse.
Once I woke up at night I've seen her on the basement door. She slowly went down and I tried to follow her. When we both were at the end of the stairs - I still wonder why she didn't seem to hear me - we both saw a mouse. I thought about how cute the mouse was. I know it's no good to have mouses in the basement but I love animals. I wanted to catch the mouse and bring her outside but before I got something to carry it in my grandmother charged at her and caught her. Then with her bare hands, she snapped the neck from the mouse and ate her.
That utterly perturbed me. She's over 70. I'd never imagined that she could be like that. She always seemed so frail. I remember the days when I was younger and would spent some time at her place because my parents were absent. The days before she killed the mouse I kind of downplayed zombie apocalypses. I mean, I didn't believe in it and it didn't scare me. I always knew the show was not real. But now... Is is normal that I fear the living deads?