What should I do. Evil boss.

So where I work my boss is super rude. To the point where people don’t come back because they don’t like her. She has a demanding attitude. We’re not allowed days off or time during work to go to appointments or anything. We’re also really short staff and she doesn’t wanna hire anyone because she’s not gonna write a check for someone who is stupid and can’t do the work. If there was ever a problem she would close office instead of hiring someone. Her words exactly. Well my sisters graduation is Friday and I was going to call out Thursday and Friday. I’m not sure if I should. She will most likely fire me because of how mad she’ll be. It would be only her in office should I just do it and call out or stay.