Come toward the jump at a canter, transition to trot and continue at the trot. Eventually when your horse is successfully jumping that way without rushing and you have the ability to canter nice and collected on the flat, approach at the canter, transition to trot and then transition to canter to the jump, canter away and then transition to trot.
DO NOT transition to halt right before the jump, we don't want to teach her to stop, do we? Take the jump and transition to halt AFTER the jump (keep things small), one rein stop, whatever you need to do, then let her continue as if nothing happened at a nice collected pace.
Use those exercises as well as trot poles and circles.