As the 3-3 defense is a kind of personal marking of all attackers, a minority situation for the defenders will be a very risky situation, as there will always be an unchecked attacker.
This free attacker can be a goalkeeper, who has been replaced by a field player. But the goalkeeper must be very aware, that when the possibility for at shooting solution is present, the "goalkeeper" must already be on he's way to be replaced by the real goalkeeper. If he is unsuccessful she must take the place as goalkeeper as good as she can. The "goalkeeper" must be on the team bench side when the goal seeking attack has started.
If the defense returns to a more ordinary defense (6-0, 5-1) it is a choice to continue with superior attack or not. But there is a risk that the defenders conquer the ball. If this happens there is a great chance that the opponent's goalkeeper or field player will try a long shot at the free goal. A little comfort could be that many of those long shots don't hit the goal.