Some mares can get very moody while in heat.
You might help her out if she is typically displaying the behavior you describe by getting the vet back out and checking her for any overian problems. I once had a nice filly who started to behave dangerously and discovered she actually had an overian tumor. Now I'm NOT saying this is the problem with you mare, but it is something for you to think about and get checked out if she is displaying this behavior regularly. There are also herbal supplements that you can purchase that will help the moodiness. At this point it doesn't sound as if longeing is the real problem, rather in its place basic obedience and respect to you and other people.