Sure sounded like her.... The credits were pretty exhaustive this episode (lookit all the Daniel Ingrams who contributed!) so if they had someone sub for her voice they would've have her credit in there too, and it wasn't.
My favorite moment was Pinkie's "Come on, Ponies! I wanna see you SMILE!!!" which had be cheering.
With a two-parter we could have seen more of the cast and town reeling from the swapping of cutie marks. In the compressed time frame it seemed like the time frame was just a matter of minutes between Twilight waking up and her figuring out how to fix everything. The whole episode apparently happened over the course of a day (from Twilight's wakeup song to the nighttime winged wonder revelation), after all. Not much time to see our heroines suffer before pulling through.