My first pony was a little welsh mountain mare, and she was the naughtiest thing on four legs! I used to finish every ride crying... i was ten. She would decide she didn't want to go somewhere, and stop, and when i tried to make her move she would rear and spin. She would rear when i tried to mount her, she would spook ALL the time, and basically she was stubborn and new every trick in the book! I had no instructot/trainer and my parent knew nothing about horses.
The only way i succeeded with her was to perservere. I NEVER gave up. She didn't want to go somewhere, I would find another way to get there. I would never get off no matter how scared I was. I would carry a crop and get really mad when she was naughty. Eventually she realised she wasn't going to beat me, and she turned into the sweetest little thing, and is now a beginners pony.
My advice for you is simply, don't give up. Ponies are veryyyy good at testing new riders, and it takes a while to get past it, as they are very clever and know lots of tricks! Be tough but fair, and be very consistent. I would ride lots of trails, and work on getting her forward. Use your leg gently, and if she ignored, more leg, and if she ignores again, very firm with the crop. make going slow uncomfortable and going forward fun. Let her have her head if she wants, go for some long canters, let her enjoy herself. She will soon realsie that riding can be fun and you are not going to quit.