Kid Decides No School Today!

I need to vent and lean on other parents for support. We have an 8yo daughter who has anxiety and ADHD. She medicated for both and 90% of the time she a “normal” kid. Today I got her up for school and she usually needs some help getting ready as she loves for us to do things for her. Well, today I asked her to get dressed and offered to help. She said “no I’m too tired.” After some gentle nudging that wasn’t working I started to get more stern. Ultimately this got me into the angry, yelling, spitting all kinds of logic Dad. I’m self-aware enough to know that is not the right way to handle anything with kids but when you sit down with them and calmly try to understand their perspective and they give you nothing it’s so frustrating. She didn’t go to school basically because she didn’t want to. This isn’t the first time it’s happened and it makes my blood boil that she thinks she can just not do something she’s expected to do. She is a strong-willed child and threats, consequences don’t work for her. Nor do awards and or “if you go to school we can go get ice cream” sort of stuff. Ultimately my wife and I feel helpless in a situation like this. How do you force an 8yo to go to school who won’t reason with you? It’s like talking to a brick wall once she makes up her mind. It makes me so angry and sad she does this.