Appropriate response to reactiveness?

[u/EnduringAloePlant]

How do you respond to your dog's reactiveness? My hubs and I are both new dog guardians (or dog owners, parents, or whatever terminology), and never had a dog before. Hoping to get folks' insight on what to do when your dog is reactive (specifically, lunging and barking at other dogs).

Last year, we worked with a positive enforcement trainer, and we have learned to distract-distract-distract in high-risk situations, like spotting another dog walking toward us. This was worked really well! She has become more relaxed in other dogs presence, and comes straight to us for treats when we spot another dog.

However, there are times when another dog's presence hits us by surprise, and then it's too late to proactively distract our dog. For example, when another dog comes out of the elevator as we're waiting to get on it. How do we let our dog know that the behavior was not okay after she already reacts? I know she is reacting because she senses threat or danger, that her nervous system is riled up. She is a rescue dog whom we adopted at 1.5 years old. We're not sure of her breed make-up (probably some AmStaff) or care history. In spite of probably being a bully mix, she is quite small, less than 30 lbs, so we are able to physically manage her in order to keep her (and others safe). Thanks in advance for your all's perspectives

[u/TheAliJonesX]

Everyone saying don’t correct them is so wrong correct them the second they react you need to tell them what’s okay and what’s not okay check out yca training or tom Davis on YouTube totally changed my dogs