Both the kicking gesture and the OP's comment sound to me like a gut reaction. The lady saw the dog coming toward her, didn't want it to, and reacted. No time to think about whether the dog was actually under control or what kind of leash was being used, etc. The OP saw the kick and reacted with what she said. Up to this point, I think that although each of them could have reacted better, I don't really see anything egregious going on.
But when the woman made the "beast" comment, she went over the line.
I was bitten by a dog when I was young and since then I keep my distance from strange dogs. (I have no problem with pets of people I know but in a situation such as this, I just, well, keep my distance.) If I felt threatened, I could see reacting, and maybe this woman did, for whatever reason, feel threatened. But again, there's just no reason to make a rude comment like that after the OP said the dog was under her control and at the point in the story at which it seems obvious that the dog was under control.