How many times? As many as you want to tolerate. If the tolerance threshold is zero, then she can contravene once and you can take action.
There's two ways a contravention order can be 'excused' - the parent had a reasonable excuse for the contravention, or the parent had a genuine fear for the child's safety, but the contravention only lasted for a reasonable time.
Can a third party be 'charged'? No, for two reasons. First, family law matters are civil matters and contraventions are quasi-criminal, not criminal, so nobody gets 'charged' with contravening an order. They simply have a contravention order made against them. Second, contravention proceedings can only be brought against the parties to whom the parenting order applies. They don't bind any third parties.