Your question is not worded that well.
Originally Posted by
bsking2
she was a high school senior and dropped
I assume this she is your sister, yet you did not say.
How old is your sister? That is an important aspect to this question.
If your sister is under 18, your father must pay your mother child support, since your sister is still a dependent, whether she is attending any school.
If your sister is over 18, but the divorce decree states he will pay child support to a certain age provided she is in school, then you have might have a case. I would think yes, since she is still attending school, but does the divorce decree state what type of school?
If your sister is under 18, has she been legally emancipated?