The shed is fine and the snake could have left a poop in it. Sheds don't always come out as an unrolled roll of toilet paper, sometimes they come as a bunched up dirty sock as you have witnessed.

As for growth, I will differ to someone who has more experience in how fast a ratsnake grows.

Also roughly how long is your snake? How old is she? What is her current weight? What size rats are you giving her? <<< I assume these answers will help determine whether she is growing well.