Joking aside, I don't know about Dahlias, but I know there are many plants that you have to take extra precautions when transplanting, such as waiting till after bloom or during a certain season. Could be over/under watering. Like I said, I don't know Dahlias, but those are some starting points till someone with the knowledge shows up.
Flower stem and leaves seemed fine and not dehydrated (I did the fold method on leaves to check).
We did not water after transplanting.
I did end up giving her a little bit of water before bed last night though. And woke up this morning to her all perked up! Not sure if the water helped, or she became acclimated, but my daughter will be waking up happy!