Thanks for the correction. I didnt think about sound being a trigger. It just seems a preferable suggestion to rewarding the agression. A behaviorist is by far the best choice as this is not really a quick fix issue.
No worries! Behavior modification works a little differently than standard training, since the goal is really to change the underlying emotions rather than the behavior directly, so you can't actually reward the negative behavior in the way you're thinking. You can certainly reinforce it with certain behaviors ("Boy, my owner freaks out when I bark at this dog, it must be REALLY DANGEROUS"), but you can't really make the dog more fearful (using fear as an example because it's the most common emotion causing reactivity) by adding a treat or praise reward.
Once the underlying emotion is changed to something more positive, the behavior actually becomes less intense and frequent on its own. You do get some dogs who learn to take advantage ("Oooh, a dog! Bark, bark! Where's my treat?") but IMO that's a huge win, because the dog is now thinking about how to earn a treat, not practicing that negative emotional response. It's usually really noticeable when this happens, because again, the barking/lunging behavior is different, less intense, more of a ritualized thing than an emotional reaction - think about someone faking being scared vs. genuine terror. At that point, you can have a lot more success training what you want instead of the barking.
Dr. Sophia Yin made a great video available here showing how pairing a negative stimulus with a reward, regardless of the dog's behavior, results in the behavior improving:
Training Aggression? Counter-conditioning a Dog to Blowing in Face
Leash reactivity is a bit more complicated than the example above, because you do have to keep the dog in that state where they CAN learn, which is typically before they go into a full-fledged meltdown over their trigger, and of course most of us don't live in an environment we have much control over once we leave our house/yard.
@Kfinch901, I wouldn't worry too much about what caused your dog's reactivity originally. At her age, when she's had a history of milder reactivity and has had a major life change that's likely causing stress (the move), it's not really going to help deal with what's happening here and now. Definitely try to stay calm when the dog is reacting, without leash jerking or shouting, but what's done is done.
I say this as someone who contributed to my older dog's reactivity through my inexperience and ignorance about socialization when we first got him. I didn't do anything majorly 'wrong' and certainly not abusive, but allowing and encouraging interaction with as many dogs on-leash as possible, combined with his temperament, and my inability to see the problem until he'd had a few years of practicing it and escalating, all tied in. But knowing that doesn't make it easier to manage and improve his behavior, nor does it really change HOW I'm doing that at all. And dwelling on it only serves to make me feel bad and actually gets in the way of making improvements because I'm focused on what I should have done then, rather than what I'm doing now. I try to acknowledge it and move forward.