Classic thoroughbred symptoms that I can relate to from my past... and Regula's comments really hit the nail on the head for me.
A horse can be good at first because it is reacting to the riding from a previous rider. So it can take a week or so for it to start acting up to your riding or handling habits.
Take a deep breath... and keep moving forward... She's certainly testing you. Following what Regula did is pretty much what I did. Also, consider turning the horse loose in an enclosed arena before you lunge to get some of the kinks out, or make sure she is turned out for the day and not stall bound. Make sure she's paying attention to you when you lunge, not just running wildly.
Just not sure you should give up yet...the rewards I had for sticking with it were amazing.