Hey Jesse, poor you, I know just what you are experiencing. My Border Collie can be quite temperamental. He likes some dogs, will walk past some without even noticing them, and will go crazy at some, as if he has been personally wronged by them!
He is our first dog, too....It is such a learning curve isn't it!
He was older than we were told he was when we got him, so he was under-socialised at that critical time.
I have tried a couple of things, with varying success.
Sometimes if I see another dog approaching that I know Jack will have a go at, I make him sit down and distract him with a fuss. This can work, dependng on how wound up he is.
I have been told by another doggy friend that walking very confidently past other dogs with your head in the air, as if they aren't there, can work: you as 'pack leader' are giving your dog signals that there is nothing to be worried about.
I was told always to ignore other dogs, and relax, otherwise your dog will sense your anxiety. However, sometimes a word of warning, like "nicely", serves to calm Jack down and he doesn't react so badly.
Jack is also fine off the lead with other dogs. I think they can feel very restricted on the lead: maybe your dog is a flight not fight type, and not being able to get away from an approachng dog worries her.
I know there are people here much more knowledgeable than me; so I wll let them give you a better answer!
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