Barb, I'm glad you enjoyed your cruise, despite the rocky ending.
I've never heard of problems with the Luggage Valet service, but I've heard of plenty of problems with airlines losing luggage.
Since it's all computerized and coded now, the airline *should* be able to find your daughter's bag. I have relatives whose bags went astray on non-stop flights, sometimes ending up in Saudi Arabia or Chicken, Alaska. If the bag made it into the airline's system, they should be able to locate it. If they have no record of that bag, it's harder to find, obviously, but they'll have folks actually looking in the airport to see if they can find it. Royal Caribbean will be looking in its luggage area, too.
Please keep us posted, and good luck.