Stepmother insists on homeschooling her 12-year-old stepdaughter because of her medical issues, going against her and her mom's wishes: 'We already homeschool our 6-year-old.'

This should be a temporary fix when her stepdaughter is too sick to attend school.

People homeschool their kids for all different reasons, and one of them is because their child is too sick to attend school on a regular basis. If a kid is out of school for "too many days" because they're too sick to attend or because they have mandatory doctor's appointments, there's a good chance their parents will have to go to court for truancy, even though these absences should be excused by the school and by the state. 

Depending on the severity and length of a condition, parents might choose to homeschool their medically fragile children for any amount of time from one semester, to their entire K-12 education. There's definitely a fine line between homeschooling because it's the only way to ensure that your sick kid will be getting a consistent education, and homeschooling a kid with a minor medical condition indefinitely even when the illness has gotten better and homeschooling for medical reasons is no longer a necessity. It's totally fine to do the latter if it's what is best for the kid and that's what they want, but a lot of kids would rather be with their friends at school if they had the choice.