I do believe she is right. In the second two clips you looked more functional than just throwing your upper body to your horses neck as in the first one.
Also, just something I noticed in the clips. Your elbows get loose before the fence, try to keep them more at your sides. This will help your upper body to stay straighter as well. By your elbows and arms falling out to the sides like that its only adding to the hunching. If you bring your elbows back to your sides, and your arms/hands steadier, it will make it a lot easier to bring your upper body back up and keep a straighter back to and over the fence.
Also, just one other thing. Try and practice waiting for your horse more. I notice in the clips that while in motion over the fence, your pelvis is appearing to be over top of the pommel. This and your form leads me to believe that you are trying too hard to jump for your horse, instead of waiting for his motion to bring you out of the saddle, and keeping your balance in line with his.
I am a big believer in the more 'functional' form of jumping.
Hope that helped! I think it is great that you tried it, that you took in what the new instructor had to say as well and weighed them both. Too many times riders get stuck in one habit and don't want to hear any other way.