I've never had Missy try herding sheep, I doubt she ever will, as I don't want her thinking she's allowed to chase anything and everything in sight afterwards.
I would get too worried that she would get hurt as well... and she's not used to being off leash yet (hopefully soon!!).
She's two and we've worked on it since a pup.

Problem is... she chases cars at the local unfenced park and chases squirrels in my unfenced backyard.
Hi there,
I know no one here knows me, but I've been coming and going for a while.
Just thought I'd give you my input on a "chasing dog" My dog, Rocket, likes to chase cars so I am very vigilant about gates and leashes

. We had cats in our home, but when I got chickens I was very concerned that he would get into the "big yard" and chase and destroy the chickens ( you may interpret this as me having absolutely no faith his farm dog instinct.)
Well, not only did he
never chase the chickens but he is their staunch defender, I never worry for them, even in the house he is on duty if they make alarm calls he fusses and frets and lets me know in no uncertain terms that he "must" go look out for them. Then he charges the perimeter or out their way for cues on which way he should patrol. Truly, he is amazing in this regard and it is all instinct. I have yet to take him to try herding but I intend to take him
soon.
He "herds" the riding lawnmower circling and barking and pushing back and forth from behind. (not while I am mowing)

but, he never ever chases
our cats nor does he ever bother our indoor birds but he
will go for a stray cat looking for a chicken snack !
I vote you give your dog the benefit of the doubt, I bet she and her heritage will far exceed what you can imagine. Though I would keep her, like I do mine, on leash when there are cars to chase.