Agree. Landing with her head down means she isn't balanced. Go back to flatwork and the basics of getting her to rock back on her hind end. Do a lot of downward transitions, canter to trot, trot to walk concentrating on asking her to pick up her forehand and getting her hind end underneath her. Work on half halts...squeeze with your leg to encourage her to get her hind end underneath her while holding with your outside hand..as my trainer puts it, act like you are a straight spruce tree when asking for the half halt..sit up straight, sink down into the saddle, squeeze to bring the hind end underneath and hold. Eventually this will lead to a more balanced takeoff before the jump and a landing with more balance afterwards. Even if she still likes to build in speed after the jump, mine used to, it will be easier to pull her up and rebalance if she understands the idea behind a half halt.