OK, well I tried asking questions first, which is new for me ... but clearly that did not work? So far "everyone in this dog's life has failed her." And you are currently working pretty hard, to be the next? If Hug's and kisses, solve dog issues? Then there would be, no need for Dog Trainers or Behaviorist?"
Having a dog with "issues," one does not understand ... is not a "crime?" It's what you do once you understand that there is an "issue," that matters. Those that "can," figure it out. And if they don't know ... "theses day's they can find those that do and just do that, if it makes sense to them.
Some people/owners only need to see what those that can do ... and that is more than enough for them, that is me. Other's need valuation from others? Before they can/will move forward?
But what does not work with a dog ... is doing the same thing over and over again and "Failing, in a new and different way!"
That is what you are doing as in well, the first "Harness did not work? But this one will be better? Well sure try that but a word of advise if you do. But a collar sung on her also and attach a D-Link or two to the Collar ... so that when she slips out of her "Escape Poof," Harness ... you will still have her!
Currently ... you are not walking your dog? She is walking you? If she is in front and pulling and putting "pressure on the leash? Then she is in charge of the walk's.
She won't go "Potty," on walks because as you and she are doing it ... she always feel's constrained? You can't say ... on walk's, go "potty," and let her feel free.
If you are not willing to "change what you are doing?" Then the best advise ... "is to hire a trainer, to teach you how to walk your dog!" Cause right now you are "messing up the first step?" In order to have "success with a rehab dog," you have to do "One Thing," Regardless of the "issue, have to know how to " Walk Your Dog!
And or if your not willing to change what you are doing or hire someone to help you, then return her before you do more damage. It can be that simple.
And that is why I quit "Fostering," it was to much "Heartbreak," for me and my wife. If I "fostered a dog," one of the first questions asked was "Can I, or my 13 old, walk this dog?" And the answer from me ... would be uh yeah? And that "Foster would be gone!" Well finding a "Foster," a new home was the point. But it was just to much for me ... so I stopped doing the foster thing, my bad?
But my point is ... if you can't walk a dog on a "Proper Structured Walk?" You will make next to no progress with anything else. And the lose dog ", BS," well every encounter has it's "variables?" But what you don't want is to have to deal with two dog's and not one!
It's another "topic," but ... what works with a 113lb Working Line GSD, works with a 10 lb Pen-Chi. Behind me dog ... I got this, it's not your problem! But if your dog does not understand there "position on a walk?" You can't do/expect that? Because they don't know ... who is in control? It's back to basics!