blueump, when it comes to exceptional substitution, there is a definite order that must be followed. Since the :ibero is still experimental this year for NFHS, we have to follow the order as given by either USAV or NCAA (since they have used the Libero for several years).
Priority for exceptional substitution is
a. by the starter or a substitute who has played in the position of the injured player, or by any substitute who who has not already participated in the game;
b. by any substitute on the bench, regardless of position previously played;
c. by any other substitute; or
d. by the Libero.
Thus, in your scenario, the lone sub (#2) is required to be the exceptional sub since she is higher in priority than the Libero (who is the very last option).