The Day My Butt Went Psycho!

Eleanor Sterne is the fictional character and heroine of The Day My Bum Went Psycho book series and its TV Series adaptation, The Day My Butt Went Psycho!.

She is a 12-year-old fierce butt fighter in her own right, Eleanor is determined to kill the Great White Butt after it killed her mother in a surprise attack on a family picnic when Eleanor was only five. Daughter of the legendary butt hunter, Silas Sterne. Eleanor is a friend of the B-team. Has a prosthetic or "artificial" butt.

The Old Butts and the Sea (Season 2, Episode 7a)
There is one scene when her a bump of her muscle is briefly shown.

The Great White Buff (Season 2, Episode 38b)
Scene where Eleanor actually had thick muscles