Legal Question in Family Law in Nevada

Probably not, at least directly and suddenly (courts are very protective of child support). I presume from your question that you have now completed paying all the alimony you were responsible to pay, and just figured this out (if not, deducting overpaid alimony from future alimony is pretty straightforward, but I would still give notice as to what you are doing).

If my original presumption is right, I would suggest a letter to your ex, clearly reciting the overpayment so she can verify it, and telling her that you do not want to have to file a motion to recover the money, etc., and ask her if she would rather send you a check for the over-payments, or have you slowly deduct it over a period of months from the child support sums you are continuing to pay (try to make it gradual), further telling her that if you don't hear back from her, you will presume that is how she wants it addressed.

Keep the copies. If she ever files a motion complaining about the support reductions, that you tried to discuss it and get an agreeemnt will probably insulate you from much by way of recrimination.