Can you describe what you mean by taking off? Falling off a dozen times is a lot and I'd hate to see you get hurt. Do you mean that she goes faster after she lands? You shouldn't be falling off her just because she is cantering fast or even galloping. Are you losing your balance on the landing? If so, you probably need a little more practice adjusting your position throughout the jump. If you are uncomfortable riding her at high speeds, then you should probably practice that as well, but without the jumping. Obviously, you want to be able to rate her speed.
But if you mean that she literally explodes on landing, then yes, that should be addressed, preferably by working closely with a trainer who can find ways of slowing her down. This might include poles on the ground, circles, and a lot of transitions between jumps. How does she do with a series of jumps? Another possibility is to let a more advanced rider jump her a few times to bring her back to a controlled pace.
My daughter's horse tends to speed up after a jump as well, and she spent hours and hours over the last 3.5 years working on it. A full cheek snaffle helped a little, but mostly, they did a lot of dressage work so she could collect him after a jump, and bring him back to her. He used to speed up because it's easier to run fast than engage the hindquarters. She can finally do it well enough to keep him under control for a full course. She has to push him forward through the jump to get enough impulsion that he jumps forward, not up, but then bring him back within a stride of the landing.