What a lovely little girl! I'm a Border Collie owner, and I see BC in several places: first, the shape and bone structure of her snoot is BC. Her back legs are BC (esp. the smaller back feet), and it looks like she has a deep chest and narrow "hips", which is typical of BCs. They are bred to run all day long, and that deep chest is what makes them so good at frisbee.
Finally, the larger, "half-floppy" ears are a BC trait. She'll be sailing through the air before too long, like a little gazelle. They really are amazing athletes. No sailing till she's full grown, though! BCs must reach at least a year old to protect them from damaging their growing muscles and bones.
Sadie is beautiful!