Is she reactive off-leash or just on it, do you know? I totally understand if the answer is, "I don't know, I don't want to let my reactive dog off-leash you nut!"
But there are some dogs who are just reactive or more reactive on leash.
Bingo. I'm afraid to find out.
Something that did jump out at me in your post is your mention of her lunging at everything and you needing to hold her with a "death grip." That isn't a good thing! She's rehearsing the lunging behavior and reinforcing it when she does it. Where does she encounter unfamiliar things? Are you taking her for routine walks?
She reacts IMMEDIATELY. And yes, she gets taken out quite often and played with daily. She's extremely hyper and needs to blow the energy! I had to teach her how to play, but she's caught on quite well and now no one is safe from the flying Kong!
She even barks at planes flying over. No joke. I live in a very rural area and she is exposed to few people. However, she also lunges at shadows when I take her out at night, jumps if I throw a stick in the brush out of the yard (when she hears it hit the leaves), etc. I've noticed a few changes lately, though and her self-confidence seems to be growing a bit with security. When the neighboring farmers feed the cows, she does more of a controlled bark, then can be easily distracted when I say, "Oh hush and go potty." She looks at me, as if the whole thing amused her. I also noticed when I had a friend over often to study with me that after a few weeks, she quit barking so ferociously and so often, instead doing a few short barks and stopping.
Obviously sometimes it may not be possible to avoid taking her out (like necessary veterinary appointments), but if that wasn't an exaggeration, I'd back off and keep working on her in your yard for awhile, then maybe start adding unfamiliar things in the yard--have a friend stand right on the edge, set up some trash cans or something if she reacts to objects, etc. Keep her far enough away that you can keep her attention, and practice walking past and ignoring them, gradually getting closer. Eventually expand it to very short walks in quiet areas, then longer walks, then busier areas, etc.
No exaggeration, trust me. She has drug me across the yard getting excited about going after a rabbit, even with a Martingale collar on. I finally did get her to quit dragging me down the porch steps but I have to tell her "wait" every single time to do so. Hence my reluctance to test her out on other people. The few people willing to do it caused her to go into an absolute tizzy upon sight or sound of their voice. She barks at dogs that are barking a mile away across the field.
Your goal with a reactive dog should be to never let them actually react--you build up their confidence and tolerance by pushing their comfort zone extremely slowly, and never letting them get over threshold (in other words, to the point where they're lunging/barking/whatever). Every time she goes over threshold, she's at best not learning anything and may even be learning that reacting is "good," because the unwanted stimulus goes away or at least doesn't hurt her.
She reacts before there is anything to react to. Seriously. She'll bark just in case something MIGHT be there. Darnedest thing I've ever seen. I know I need help with her to pinpoint timing and techniques but my job just got outsourced and I'm pushing it right now to keep a roof over our heads. Overall, this dog has made huge improvements, though, and she's becoming a quite enjoyable dog in my home. She was almost like a wild animal when I brought her home a year ago.
Sorry if that is presumptuous and you already know that, like I said it just jumped out at me in your post. I'm glad you had such a good experience letting her off leash in your yard!
Oh, I appreciate the input!