$400-$600 per person x 3 persons is what the OP is asking, that is $1200-$1800. By my estimation, that is AT LEAST half the total cost of the trip for three people.

I was trying to point out to her that while it is inconvenient to be delayed by a flight, it could have been worse - at least she was ABLE to fly wherever she wanted whenever she wanted.

And bottom line, being delayed by a flight for mechanical problems IS NOT cause to demand up to half the cost of your vacation reimbursed. She only missed 5 hours out of FIVE WHOLE DAYS!