Hi, virtual school teacher here with thoughts. You said it was a charter, so if you're in the US that automatically means public.
You said she was just diagnosed. Was this diagnosis shared with the IEP team? If you have any interest in staying with this school, this could help with new accommodations to help her with lesson completion.
The way she's been completing lessons sounds reasonable at least to me. If that method keeps her on track and doesn't affect the integrity of learning and practicing the material, I don't see what the big deal is. That very way may be great accommodation for her.
That all said... A huge majority of accommodations in virtual school tend to fall on the parent and virtual school requires a lot of independent determination from the student and family.
In my state, any public school including charters has the right to deny entry to an expelled student for up to a year, so if it comes down to it, yeah, you're best to withdraw on your own.