Iris (my German Shepherd) does excellent in Agility and I don't see why you can't do Sadie in it. She also does great in Obedience.

I actually know alot of Border Collies and Aussies that don't do so good in agility because they go TOO FAST!!!

Iris is actually amazing because she had femoral head ostersecmony (spelling?) a hip realated surgery. So now she's kind of a 3-legged dog and she does agility!

You can goHERE to see pictures of Iris doing agility.