Start from a pole and do it both ways. Then raise it. And jump it. Both sides. And again until she refuses, at that point you simply do a change of direction and send her to it the other side and she will jump it and you change direction again and she refuses and you change direction and send over the jump the other way, you keep repeting until she jumps. Once she has you stop her.
I'd say flatting the hard way much more often. Horses, like people, have a dominant side so you have to make sure the muscle building and the amount of work both ways is even. Horses can't be expected to jump well on a side that they are unbalancedon!:)
I used to ride a horse that he was a bit scared of jumps and he had the same problem. It was because he didn't "recognize" the jump taking it in the other direction. I recommend you what Andrew said and maybe start jumping her as a groundwork excercise first and see how she's doing, then try to jump her while riding.
I hope you can fix it ;)
My mare was really good to the left and awful to the right for a long time and what I did for like two months was every time I wanted to jump for every five jumps to the left I did, I'd do one to the right. And if she did it well and quiet I'd stop and end the ride there as a reward.
Just had the vet out today to check her out ( and an old ingry )for any problems and she has a full bill of health. Totally healthily, I asked him if she's save to learn to jump and he said theirs no risk so i know this isn't a vet related problems.