Hello, my name is***** and I have over 20 years of experience as a veterinarian. I understand that you are concerned about your dog's behavior around the kittens now that they are learning to walk.
Your dog's behavior is upsetting but it is understandable. Some dogs have more advanced hunting instinct compared to other dogs, and these pups will instinctually respond aggressively to young animals that look weak or move like prey. Of course this is exactly how young kittens look as they struggle to learn to walk.
Instinctive behavior like this makes the dog a terrific hunters if they have this sort of instinctive behavior as well as they ability to learn to hunt. There can be a very strong prey drive in some strains of dogs that is almost automatic behavior. There are certain stimuli and cues that they respond to, and are almost unable to help themselves when they are exposed to them. I suspect that this is the case with your dog. For whatever reason the way your kittens behave and move triggered instinctive behavior in your pup. These "cues" can be the sounds an animal makes, the way it moves, their size, and scent.
She is not a bad dog necessarily, and I would not expect her to be aggressive in other situations, but I would never trust her around small animals, including kittens, small puppies, pocket pets like hamsters or rabbits, or even a human baby.
You can consult with a professional trainer or a veterinary behaviorist to try and change the behavior, but there is no guarantee that it will be effective and I would never feel 100% secure even if she seems to improve.
It may be once the kittens learn to walk properly and mature a bit she will be fine with them. In the meantime it is essetial to keep her separate from the kittens, she simply cannot help herself.
Knowing her nature I would not ever leave her outdoors alone, and I would be very careful with her on walks, making sure you have full control at all times.
If you want to read more about predatory aggression here are some very good articles about it and possible ways to deal with it:
I know that you may be feeling very surprised and possibly emotional now. Please know that this behavior is an extreme of normal, and does not make her an aggressive or bad dog in general, just one we need to be very cautious with.
Please let me know if you have any further questions.