A couple things.
"Reactive" is next to useless once you start getting into details about how to address it, because it can cover both a wide range of actual behaviors (from barking and pulling to serious snarling, lunging, redirecting bites onto the handler) and a wide range of underlying causes (alertness/interest, excitement, fear, predatory drive). Dealing with a dog who has some naughty leash behaviors because they're excited or alert to environmental changes, but aren't super emotionally amped up, is very, very different than dealing with a dog that is having an intense emotional response to the trigger. In the former case, yes, often teaching the dog what you DO want them to do in that situation, and reinforcing that alternative behavior can be really effective. You have to take a completely different approach to a dog whose emotional state is so charged that they physically cannot process input from their handler. Telling someone with the latter scenario to just fix it as if it were the former scenario is setting everyone up to fail.
Point is - assuming one "reactive" dog is having the same external behaviors and/or internal emotional state as any other "reactive" dog is silly, as is assuming that what works for one will work for all dogs one can possibly label "reactive".
Secondly, even when reactivity is undeniably caused or worsened by the owner/handler, it's a pretty darn useless thing to point out. Hi, I'm an owner who absolutely set up my first dog to have reactivity issues, and am now dealing with the consequences. Understanding that I was part of what created this problem does absolutely nothing to improve how I work with it now. Understanding <i>what</i> I did helps a little, but it's still much more useful to inform how I handle future dogs, rather than change how I'm currently managing and working with the reactive one. Yes, being alert for triggers and being proactive with putting distance between your dog and it - as well as getting as much engagement from your dog as possible - helps, but acting like this is ALWAYS possible in the real world with a dog who has serious emotional responses to their triggers is. Silly.
Example: I was loading up my reactive dog into the car a few nights ago. He was sniffing something with his back to the end of the driveway. Suddenly a Tervuren just pops up from behind the bush (on leash, but the handler was a few steps behind and not immediately visible) at the end of our driveway, not three yards away. Waaaay inside my dog's threshold, and he does worse with 'surprise' dogs (as opposed to when he's aware of them at a distance and they approach) and in the dark. Luckily I was able to get him in the car and tethered without him spotting the dog, but only because his back was turned when it appeared. No amount of me being vigilant and proactive could've saved me from a blow-up if he'd been looking in the same direction I was. I'm not always this lucky, and very few people have the luxury of living somewhere so quiet or remote that they can reliably avoid their dog's triggers surprising them. The fact that I can't always prevent reactivity doesn't mean I'm a bad handler, or that my current approach to working with him is wrong, and it's more important to empower people dealing with these frustrating issues than guilt them.
To more directly answer your questions, @visualbread
, is there any way you can exercise her without walks for a while? Access to a yard or other safe, enclosed outdoor space where you can engage her in some active play, do some more physical training, that kind of thing? That would be ideal, so that you can always keep leashed walks as training time, and it's okay if you don't get very far. If you have space but it's not big enough to be her only physical outlet, some more vigorous play before walks might help take the edge off her excitement - just know that some dogs need time to cool off after high-energy play to come back down to a calmer space, while others can go right into a calmer activity.
The alternative I would choose if non-walk exercise isn't realistic (as someone who's rented the entire time I've had dogs and knows safe, fenced outdoor spaces aren't always easy to come by) is to have two pieces of gear on the dog. When you're training, you have the leash attached to one (say, the collar). When you're done the training and just need an exercise/stimulation walk, switch to the other (say a front clip harness). The gear you're actively training with should be what you want to be able to walk the dog on long-term. Hopefully, you'll slowly be able to have her go longer and longer on the collar, and she'll learn that she has to mind her manners when she's hooked up to her collar, even if she can be nutty on harness walks.
The issue with other dogs may need to be addressed separately to her walking manners in general, for all the reasons discussed above. Emotionally driven behavior is harder to change, especially if she's had a long history of doing this. I like Patricia McConnell's "Feisty Fido" book as a primer about why dogs can be leash reactive and what to do about it, and her "Cautious Canine" addresses fear issues more generally - she also has some free blog articles on the subject of reactivity and dog-dog aggression. For something more in-depth, Grisha Stewart's BAT 2.0 was a really informative read for me, though it's much more technical. I don't have the resources to do her full BAT 2.0 program (it requires lots of space and easy access to human and canine 'helpers'), but there was a lot in there that I could apply to managing and working with my leash reactive dog. "Frantic, Fired-Up, and Freaked Out" by Laura Van Arendonk Baugh and "Control Unleashed" (I think 'from Reactive to Relaxed" is the most recent version) by Leslie McDevitt are also great options if you're looking for more in-depth guidance without the cost of a professional behavior consult (which are also an option, but the books are a great first step).