Join ReactiveDogsUK on facebook... honestly it's a sanity saver... huge amounts of professional force free advice, and a very supportive community.
And they will point you in the direction of a recommended force free behaviourist in your post code :)
Also have a look here:
careforreactivedogs.com/start-here/ Have a good read.. this is basically the approach you need (and it's a bit more in depth than see a scary dog, pair with treat, because distance and timing is crucial)
And... don't despair! My girl is 3.5 years old now. At 1, after a bad experience she became very very reactive to pretty much all dogs (inc her previous puppy friend), any men in black, anyone coming to the house... there was a long list, which grew every day. I was so upset that my previously happy girl seemed terrified of everything.
Several things helped: RDUK, CARE protocol, and time and space... lot of opportunity to NOT need to react: so we did long country walks, we handled visitors carefully and practiced having people knock at the door.
Now she's not perfect... there are a few breeds she reacts to(huskies, Italian Spinones and most spaniels!) but she is 90% better than she was even a year ago... she has matured and she has learned to trust me, do a swift turn and take a treat while retreating if we see a dog I know she might react to...and the rest she manages to pass or ever say hello to!
Like yours, mine is fine with her dog walker's gang.. (even a husky.. she has great play chases with him) because she knows them, so they are predictable.
I really thought mine would be uber reactive forever, but now she's just a bit of an asshole at times, which is a huge improvement.
Good luck :)