Ball Hit on Opposing Side

[pavbref]

Assuming that you are referring to NHFS rules.

She was called for illegally crossing the plane. The R1 told the coach that her player had "attacked" the ball, which is illegal. His determination was that the although the other team had already had their 3rd hit, the ball was attacked and not blocked.

Per rule 9-6-6, blocking a ball which is entirely on the opponent's side of the net is permitted when the opposing team has had an opportunity to complete its attack. The attack is considered complete when the:
a.) Attacking team has completed its three allowable hits;
b.) Attacking team has had the opportunity to complete the attack or, in the referee's judgement, directs the ball toward the opponent's court;
c.) Ball is falling near the net and, in the referee's judgement, no legal member of the attacking team could make a play on the ball;

The block is defined as you referenced as long as there is no prolonged contact. An attack is defined in 6-5-1b as any action other than a block or a serve that directs the ball toward the opponent's court.

In the situation described, the action was a permitted block unless there was prolonged contact. The R1 used a wrong interpretation of the playing action in my opinion.