Pony very fast trot, head high and ears back?

Hey! I have recently bought back my pony. When I owned her years ago she was always very whizzy. She hasn't been ridden much in the last couple of years and found that she is still very whizzy, if not worse. In her trot, her ears go back, she holds her head extremly high and her trot gets faster and faster whereby it is nearly a canter. I remember I used to continually squeeze and release the reins and keep her on a tight rein whilst in trot however someone has advised me to give her long rein as she is trying to get away from the bit? What do you think I should do? What bits would you recommend. She is on a straight bit at the moment with a chain, sorry don't know technical name, its what came with her bridal when I bought her. I tried riding with a very long rein, when walking her head came down and she seemed more relaxed however in the trot as she got faster I lost my balence and felt the only way to slow her down/stop her was to get my reins back. x