Online schooling?

My sister just moved back from oregon to michigan a few months ago. She was there for 4 years with her mother. She started in a new school this week as a junior. She wants to finish her classes online and graduate asap (straight A and B student) so she can work more than 20 hours a week. She wants to have 2 jobs and save up for a car because my parents didnt sign her up for drivers training in time because she "didnt want to be part of the family." Not to go into my family history too much but its very disfunctional and i personally cannot have a conversation with my mother without it being about someone elses drama or what she wants ME to do as a person ( im 21). Also a conversation came up a week ago that the family is only functional without us in it. Im in group therapy for this right now because it really hurts me to hear that from them. If my sister has the ambition and drive to do this is it fair for my parents to keep her in school? Ive been looking online and i believe i can sign as her guardian to help her out.