Yeah, and they could have even done something like having the Lanister army blend into the crowd, holding them hostage while threatening to blow up part of Dany's army using wildfire explosives, or a hidden Scorpion aimed at Drogon, etc.
Her insistence on targeting the civilians as if they're more of an enemy than Cercei made the whole thing make even less sense.
Nah, that would be what every other ruthless and calculating leader would have done. The thing is, Dany was never build to be calculating. Her character has been very different from others who wanted the throne.