My wife was acting pretty immature while she was waiting in line at Disneyland.
What is your reason for feeling that she was acting immaturely?
She complained without reason and she kicked the back of the people in front of her.
That sounds pretty childish of her! I think you do need to let her know that she was being rude to other people and that that's wrong. Hopefully this was just a one-time incident!
She needs to stop and grow up.
Well it is good that you let your wife know that she was acting immature. There is no reason why she should ever kick the people waiting in front of you, as this is just going to make those people upset.