NFHS Unreported Substitute
 

First offense:
If the unreported substitute is at bat or has completed her turn at bat we just enter her into the game. That is clear. Plus the team warning.

Second offense: Since the player will be restricted ...
If the unreported substitute is at bat, offense must either [a] put in an eligible substitute, or, [b] if no eligible subs available, the batter is out.
If the unreported substitute has completed her turn at bat and is on base, then [a] same as above (case book 3.3.8.A, p. 26), or [b] the previous batter not on base can be used as a temporary runner (case book 3.8.8.B).

Correct?

Eligible substitute can be the player substituted for, given re-entry possible.