I think also because various features can modify the critical damage, like dealing extra damage dice after critical, or perhaps later on there will be a feat tripling damage dice instead

why this part "using that focus to cast spells would count as holding the Thunder Crystal" included? To use focus, you'll need to hold it in your hand, so why this part specifically calls out that? Can you use this crystal as focus without holding it - but need this part to specifically let it as if you're holding it?

To clarify, you mean accurate weapons - like dagger and shortsword feels too similar because they have same/similar attack dice and success range? How many weapons do you have planned? There are not so many standard weapons in 5e, with only up to 6 (CMIIW) weapon properties and they feel quite distinct from each other

Do you play fully remote? Or you are beside her while Zoom-ing? If yes, do you have separate laptops? What distractions do she notice herself? Is her on medication? What part of the game when she got distracted? Do other players notice this? Do they complain? What part of the game do you think you need more cohesion of? Combat? Roleplay? I think we need a lot more information instead just throwing general advice?