I am so burned out! Is it selfish to find someone else to care for my nan?

I'm the sole caregiver for my 85 year old grandmother. She is very demanding & difficult, passive aggressive, verbally abusive and has to be the center of attention at all times. She is able to live independently without any outside help but she refuses to do so. She expects to be waited on hand and foot. I see her twice a week right now for a few hours each time and I feel like I'm having to walk down death row every time I'm expected at her house. I've been caring for her for 2 years and I'm so burned out. She can be sweet at times but usually only reserves that for everyone else outside of our family but people over time have come to understand her personality. She has zero friends! I feel so guilty for feeling the way that I do because she's the last link I have to my dad, who died when I was 11. Usually I can emotionally distance myself from her but lately it's become too much. My mom, who is only 60, fell and broke her hip last week and had to have a hip replacement. I've been going to her house every day for a few hours to help because my stepfather owns a business and works constantly. I'm a young mother to two young children. We have animals & property to care for. I have my own mental health issues that get in the way of my own daily living and pushing myself just to get out of bed and care about the day is a chore. I'm sorry to whine because I know it could be worse but I am just so overwhelmed and I don't know where to turn. Is it selfish to find someone else to care for my nan? I love her like crazy but I just can't deal with all of the stress anymore. :( Thanks for listening.