Mixed Australian cattle dog with… something else? pure or not?

I’ve adopted this beautiful girl about 3 years ago. I never cared about breed, but people keep telling me she’s “pure breed” and then someone comes and says “she’s mixed”. Even her vet said she’s pure and then another vet said she’s probably mixed. She was abandoned on the street by her previous owner so I can’t ask that. Her fur grows to be very long, specially around the neck, and her ears aren’t pointy and straight up. That’s all I can point, but people tell me that Blue Heelers always have short fur and pointy ears, so…? I don’t know.