[jimworcs]

If PHXflyer has looked into this and determined this was a chaotic day for weather delays in ATL then it is likely to be an uphill battle to prove Delta are exploiting this to deny a passenger their rights. I think the only option is going to be a complaint to the DOT and perhaps a small claims court. You will need to gather as much evidence as you can.. in particular, the exact time of landing (try Flightstats.com) and the time the flight she was meant to connect to actually took off. If you can establish that these flights were not weather affected, you may have a reasonable case.

Delta may claim that the chaos generated by all the other delayed flights which were weather related meant that there was no gate for your flight and this is why your flight could not disembark. In other words, the delay was weather related but that the delay was on the ground. You would have to have some basis for refuting this and might want to talk to someone at the DOT regarding their rules in this situation as I am not sure if this would be considered a weather delay or not.