What should I do about this horse? Please help!?

I just bought my first horse. I'm a seventeen year old confident beginner rider. The woman I bought my horse from used her as a kids lesson horse, said she was dead quiet, 'too lazy' to use in lessons, a 'dead horse', etc . I paid 1000 dollars for her because she sounded perfect, and behaved perfectly when I rode her and when I brought a consultant who rode her as well. I keep her on my nieghbours farm for free, and our agreement was a horse that was okay for small children to ride (for her young daughters). The woman I bought the horse from knew this. She also knew that we had no ring of any kind, she was just gonna be ridden on trails, hacks, and in the pasture. She ured me she was not spooky, a perfect horse for a beginner, only needed a soft snaffle, I could put my non-rider friends on her, etc. Well. We brought her home monday morning, I didn't do anything with her until tuesday afternoon, I just brushed her a bit. This morning I brushed her for about twenty minutes, then my neighbour thought maybe I could go for a quick ride because she was really calm and looking settled and happy. So we tacked her up western. First my neighbour used a leadline and I pony rode for a few minutes in the driveway, then she said I could go up the lane alone (Keep in mind, the woman I bought her from knew I wanted a horse that I could tack up and take out on my own). So I started riding (it's a pretty long lane, I never got to the end of it...), just walking, I thought I'd trot on the way back but walking was fine by me. Eventually she started to try and trot, so I kept pulling her back. I thought she was just excited to be in a new place.She kept doing this, and then she started throwing her head way up (no martingale or anything, she ured us a snaffle would be fine) and she wouldn't stop! I could not control her at all, it was like there was no bit in her mouth! Then she started cantering. It took me a little longer than it should have to realize soomething was definately wrong, that she was not just a quiet old mare (She's seventeen years old!). I was worried she might buck, plus she kept trying to go faster, so I yanked her head around as far as I could. It did nothing. She hopped her hindquarters to straighteen herself out, and then took off at a full gallop off the trail and into a field! I have NEVER galloped on a horse. I've never even cantered except in a ring! I was SO scared. I knew screaming for help would just scare her so I just was like 'Easy, girl! Whoa!' or whatever and just trying to hold on. I tried sitting back and pulling her back but it didn't have an effect on her, so I just focused on holding on. Then she went over the fenceline (thank god there was no logs, barbed wire, etc) and back onto the trail. A couple feet ahead there was like a four ft long puddle, and she JUMPED IT! Like 2 ft or more off the ground, all the way across. I have only ever jumped a 1 foot cross pole fence years ago! I got booted in the tummy with the saddle horn and almost fell off, but luckily I regained balance. By now we were almost home, and luckily she stopped right in front of the pasture. I was so much in shock. I just hopped off, walked her over to my neighbours house and told her daughter who was playing on the deck to run and get her mom, QUICK. I was okay but it was the scariest experience of my life. My neighbours husband rode her afterwards and she took off galloping up the road with him! So it wasn't just me. When I got home I called the woman I bought her from and told her what happened, and she thought it was perfectly fine!! She said 'oh its cuz shes new, she probably panicked in new surroundings'. She did NOT look like she panicked. she made no effort to buck me or anything, honestly, she looked like she was having so much fun! Probably first time she galloped with a rider in months instead of being stuck plodding around a tiny arena. She also was like 'Well, i didn't advertise her as a trail horse!' but she knew thats what I would use her for and said it was fine! I really do not think I should keep this horse. She is not at all a 'safe kids horse'. I just need guidance. The woman doesn't want to buy her back, even though supposedly she had '5 other people who wanted her and would pay more'. I don't know enough about horses to sell. I'm so scared financially. I paid for her myself, I work part time at mcdonalds. Getting a trainer or riding lessons is out of the question! I just feel so cheated and angry. Does anyone have ideas? Thanks