I read somewhere that getting dresses made at a french fashion house was always going to be high risk for the amount of time/number of fittings they would have, but Meghan had her heart set on it.
It sounds to me that Kate probably had a sound knowledge about protocols, tights and made to measure clothing etc, but Meghan thought she was just creating problems - hence the falling out at the fittings and down the line when the dresses arrived and needed intensive adjustments at the 11th hour.
However frustrated/upset Meghan might have been at the time (both about wedding plans and the stuff with her dad which she alluded to in the Oprah interview) I suspect Kate has been unfairly maligned for trying to keep things on track.