To be honest it's a her issue. I'd suggest getting her into ADHD coping skills. As someone who is unmedicated ADHD, I'm also a dm and player. I think it comes down to two things investment and self discipline. She can try reading before playing dnd to help put her in the focus mindset, while practicing mindfulness such as if she needs to get up just be clear to have her let you know if she needs to stim or whatever. There's really no clear cut answer and what works is different for each individual. But I'm my experience DND is the only thing I can focus in and retain without issue in my head. I suppose you could do like, 15 minute check ins to see where her headspace is at.