STOP TAPPING and begging and just 'pecking' on her to move. Be more like the boss horse in a herd that would dive at her and take a large chunk out of her butt when she refused to move when told.
I would first ground drive her in long reins. I would ground drive her out in the open and MAKE her go over logs, ditches and anywhere else I could find that she might not want to go over or through. I drive them up and down pond dams and over creeks.
1) I ASK by smooching and lightly slapping the reins on the sides of one's butt.
2) I TELL by slapping them harder or taking the ends of the long reins and hitting them pretty hard with them.
3) I make their live plum miserable and make them want to get the he!! Out of there to save their lives. This, on occasion, has meant that a second person has taken a rawhide covered stock whip to a really spoiled one that was backing up and trying to kick our heads off. They have ALL figured out they should go forward anywhere we want them to.
Then, ride her the same way.
1) Ask ONCE by smooching and tapping her butt.
2) TELL her to move by hitting her harder on the butt.
3) Make her move that butt by spanking her HARD on both sides. Make her think she is luck to be alive.
I, too, use long harness leather reins. They are 'weighted' by being thick on the ends. I buy them from an Amish man that cuts them the full length of the hide with the ends being cut over butt where the leather is about 3/8 of an inch thick. [He also makes 'cowboy style pulling collars', headstalls and hobbles for us out of heavy oiled harness leather.] When you use and 'over and under' style of 'driving' a horse forward with them, they will leave welts and the horse WILL go forward.
If a horse is very spoiled (and this one is), all pecking and nagging does is makes them more resolved to will the battle. While horses do not look at refusing to go forward as 'getting out of work', they sure learn to look at it as a 'battle of wills' that they can become very determined to win. Some horses will 'work' hard enough at trying to NOT do something, that they will work themselves nearly to exhaustion fighting it. Sometimes you can just outsmart them and make the right thing easier and other times you just have to show them that bad behavior hurts and they can't win.
I have seen Parelli Horses like this that had done 'ground work' and 'played games' for many years and during that time, had refused to be ridden at all -- just like this horse. This is why I say that going 'back' to ground work is not always the answer. Some just need a good rider that does not put up with any BS from them. That's what this horse needs.