It is unfortunate that the OP was not aware of all the issues that can arise during airline travel that could effect her underage daughter. This post was good in the fact that it will educate parents to be aware that unless you pay for your child to have underage priveledges they will be treated as a regular passenger in terms of bumping priority.
My point is this, if you are buying a ticket on an airline and NOT informing that airline that you have an underage passenger, how are they supposed to know this? Look at it this way, on the airlines it is all about fare class. They have multitudes of codes to determine your priority on the flight. People may not be aware of this, maybe they are. People paying the lower fares have a lower priority. That is a fact of life. The airlines have a policy in effect to give underage passengers special priveledges. They charge a fee for this. Every single thing the airline does that is 'extra' they charge a fee for. The airlines also have a policy in effect that does not permit unattended children to fly on the last flight out of an airport. Again, they need to know you have an unattended minor flying to inform you of this.
Regulating something that is already being handled by the airlines seems like overkill to me. If the airlines get enough pressure in regard to this, they will just forbid anyone under 18 to fly without an adult.
I guess my question is, if you have a child that you don't want to be subjected to all the things a normal airline passenger can be, why not pay the $40? It would seem cheap to me to get the peace of mind that your child would be on the flight. I mean Southwest makes you buy 2 seats if you need them, airlines charge to give your child sprecial boarding priority. It is basically an insurance policy. And just in case people are wondering, paying this $40 does NOT mean there will be a babysitter sitting next to the child on the plane. It means that there will be an agent there on the ground to make sure that they make connections, make sure that the are not bumped and make sure that they are not stuck in a city overnight.