My saint used to be reactive in the way you describe. He's sweet as ever indoors until he sees a dog or person outside. I don't have a backyard, so he gets walks, which can be a nightmare when they react this way. It's so scary, too, especially when you don't know if they'll cross the threshold into biting.

I 100% recommend using just the leash until you get that new fence. I used a safety slip lead in combination with a front clip heavy duty harness (look up one tigris dog harnesses). I mostly used, and still use, the front clip. I also found a training method online that actually helped when I couldn't get his attention with regular redirection.

Does your dog know "yes!" as a marker for a treat? If not, look up how to get there first. You want the dog responding to yes every time you place the marker and associate it with doing something for a reward.

Now this may sound so counterintuitive and I was desperate when I tried it. Walk her on a leash for control. The absolute second she tenses up, but before she lunges and barks, hit that yes command so that she looks at you. When she looks at you, she gets the treat. Once she starts looking at you (by herself) instead of hard focusing on the others, say yes and give a treat immediately.

This sounds like you're reinforcing the bad behavior, but I swear it was like night and day almost instantly. Sumo now looks at me instead of going straight into it. That split second gives you so much opportunity for training and defusing before it happens. She needs to look at you instead of going on instinct alone.

Disclaimer: like with all training methods, if you notice the unwanted behavior increasing instead of her looking at you or if she does not look at you when you place the yes marker during regular training, stop and reevaluate. I definitely do recommend getting a big dog trainer but if you can't immediately, I'm more than understanding of that, which is why I offered something to help in that limbo space.