Since your daughter is still in high school, it does not matter that she is turning 18. You must continue paying your child support until she graduates (or turns 19-1/2 years, if that happens first). Once she graduates, your child support will terminate.
The way you have worded this question, it sounds as if you are the parent RECEIVING the child support. You have read your judgment right; your ex is required to pay until she graduates from high school, even if she has turned 18.
If his support is being automatically sent from his wages to the Friend of the Court, you should not have a problem. If he is paying you directly, and he stops because she has turned 18, you will have to take him to court to force him to continue to pay and to get an Order of Income Withholding so that your support comes through the Friend of the Court.
If your support is being paid through the Friend of the Court and it stops coming before she graduates; be sure to contact the Friend of the Court to let them know she is still in high school. You can do this anyway if this is something you are worried about.
I hope I understood your question correctly. If not, please feel free to contact me.
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