I think I can piece together what happened from the information given. The OP stated she (I'm assuming gender here) paid them "$100 for them to walk her to her flight in Atlanta" which is Delta's fee for unaccompanied minor service. She mentioned flight 1476 from Kansas City (MCI) to Atlanta and flight 1672 from ATL to Jacksonville (JAX). I looked up the flight status for DL1476 today and it was severely delayed. Scheduled to depart at 4:29 PM it didn't leave MCI until 7:21 PM and arrived ATL @9:48 PM nearly 3 hours late. The two remaining flights from ATL to JAX were DL 1672 with a scheduled departure time of 8:17 PM and DL 1263 @10:50 PM. Both of those flights were delayed as well. There was weather in ATL this evening when evening thunder storms rolled in.
Now when the daughter's flight left MCI there was no way of knowing if they would connect to 1672 because they would already be past the scheduled departure time and since iot was a weather delay it could have been cleared to depart at any time. The only connection she could have made was the last connecting flight of the evening. Airlines will not book an unaccompanied minor on the last connecting flight of the day to avoid the risk of the minor being stranded at the connecting city.
So, Ms.
rosemcelhi, you go on a tirade about how awful Delta is by denying boarding to your 15 year old daughter while all the while they were looking out for her best interest. Was this not explained to whoever took her to the airport in Kansas City? What if they had allowed her to go to Atlanta and the flights to Jacksonville were canceled? You would really have a reason to complain then and I'll bet instead of going online to lodge a baseless complaint you would be on the phone with an attorney to start the ball rolling on a multi-million dollar lawsuit!