ROTFLMAO!!!! I LOVE the first picture LOL!!!!!

Anyways, by the position of her ears and the way she sits, I'd definitely say part Whippet or Greyhound. Do you have a picture of her standing from the side (profile)? As well, what is her height and weight? I definitely see the ACD, but chances are she's probably more than an ACD/Whippet mix. Probably some smooth Collie. Whatever she is, she's beautiful and it sounds like she'll be a champ in flyball! Speed and versatility meshed into one dog.