Skip the testing and look for accommodations that you can do. I know a diagnosis is helpful, but it is not the end of the journey. It’s the start.

There a lot of good resources online (like How To ADHD on YouTube) that can help you find ways to improve her life. There will be some trial-and-error; ADHD is not a monolith. And doing that, she might come across information that will demonstrate to her that does / does not have ADHD.

Some of the advice can also help neurotypical people, so even if she does not have it, it might still help her.