My horse rushes her jumps!?

me and my ex-racehorse mare have been jumping this week after a week of trotting poles and cavelleti. She just takes the bit (plain snaffle) and pulls and pulls. I feel as if I have NO controll and its starting to knock my confidence. She rushes the jumps and rushes after. She has a martingale on because she sticks her head up and hollows her back which makes it even harder. Plllleeeeaaasee give me a hand?