It’s a common problem with teens, to refuse ADHD medication, but, of course, it happens at other ages too. You might find the advice in this article useful for your situation, even though it’s written for teens:
It’s much better to have collaborative discussions with her about why medication is useful and why she doesn’t want to take it, versus trying to force her to take it. The first will be much more well received.
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism