I know a little bit about what you are going through. My husbands ex is a walking nightmare and she, too, took his/their daughter out of school to be homeschooled by her aunt. The ex did this without my husbands consent. Well, she finally went back to a public school about 3-4 years ago and was held back a year because the "homeschooling" didn't go well. My step-daughter is 14. We live in Indiana too. Coincidence!

Anyway, my husband hasn't seen his daughter in 2 1/2 years and we just started receiving school and medical records. Her grades are terrible. She's getting 4 d-'s and she's been late to school 16 times so far this year.
I read somewhere that the non-custodial parent must also give consent to have the child homeschooled or support would still be collected but set up in an escrow account until the mother or CP re-enrolled the child in a regular school. I DON'T KNOW IF THIS IS A LAW OR JUST A BILL TRYING TO GET PASSED! I would call an attorney specializing in family law and see what you could do. I'm under the impression (but I could be wrong) that regardless of whether your SD has a diploma or not, CS will stop when she turns 19 if she is not going to college. Let's face it, neither yours or mine has a snowballs chance in hell of getting into college! But, if your SD isn't living at home and is working to support herself, I would think that's called emancipation. And that means no more support! CALL THAT LAWYER. Make sure they are very familiar with family law. I will be very interested in knowing what you find out. Please let me know. If you would like to talk, let me know and I will give you my e-mail address. Good Luck!