sorry but do you know about
1. a story in which there is a chapter where twilight dances horribly and comes back with a sore applejack and then princess Celestia tells her to do some sort of different dance form and everypony watches slack jawed at how a pony who was dancing so horribly then was dancing with such skill now
2. a story in which twilight's mom is a real jerk and berates her about her inability to bear children due to turning into an alicorn and when twi explodes saying that she would prefer princess Celestia as her mother, she goes to the palace to shout at her and without thinking utters the term mud pony and is banished to ponyville
if you do please inform, i cant find them at all !!!!!!!!
thanks

Second one sounds like Rites of Ascension, no idea on the first one.

7355015
Was that 'Rites of Ascension'?
I had forgotten where it came from, but I still remember Velvet inadvertently calling her daughter and the princess 'mud ponies' to their faces.

7355128
Its in the chapter "good for the goose"

I know that this was written a long time ago. But I actually have the story in which twilight actually dances pretty good. It's called "Opening Celestia's Heart." I don't know if is the one that you say. But a fair warning,it is actually a Twilestia story! The part in which Twilight dances with Celestia is in 'Chapter 8'. In which everybody tries to stop Twilight from dancing, but Celestia still danced with Twilight. Hope I was of help and please message me if that was the story you were trying to find... Crossing fingers that this helped you!