My female Shepherd is reactive so I have some experience (although by no means am I an expert). I will answer the last question first.... yes, the positive, feed treats training can work, but I am sure there are many different views on this. It worked for me and my dog.
However, I would definitely say you are not wrong to cross the street. I still cross the street when I see people coming towards me with my dog. It is not necessarily that Willow will react, it is that she definitely won't react as long as there is that distance between two dogs.
Not sure how far along the boxer lady is on her training but in my experience the process to work through reactivity is long and tedious. Every walk is a training session, not just a jaunt around the block for exercise. As your dog gets older, you may offer to help with her training. The hardest part of our journey was finding training partners with non-reactive dogs that I could use along the way.
And my Girls.....
Dallas - ACD mix, 11 yrs
Willow - GSD, 5 yrs, CGC