I rode another horse (a trakhener) for a friend and that horse hadn't had a round jump in his life. Like your mare, he's a pogo stick. He's got an amazing hind end that can get him out of anything and his front end just goes to hell. He has a very flowy way of going which made him nice to watch; therefore he was competitve in the lower level hunters. When I started riding him, he had been out of work for a year or two and the time off really was not good for his confidence. Needless to say, the timing was never right for this horse and we never found the height that made him use himself.
Agree with Kryswyn- she is purposely bred for dressage and she looks like she'd make someone very happy as a dressage horse. Why not sell her as a dressage horse and just purchase something bred to jump?
Additionally, four is young for a warmblood to be really jumping...they mature more slowly than Thoroughbreds. She may not end up being a good jumper or she may end up being better with correct training and age. While it's great that you've spent the time with a dressage trainer getting her flatwork basics down, if you want her to better develop into a hunter, you should start lessons with a hunter trainer instead or in addition to the dressage lessons.
If you really like the horse, keep her for longer and either start lessons with a hunter trainer, send her to a pro for training, or take her for pro rides once a week. See what she develops into.
If you would rather have a horse that's more of a sure bet for competitively showing hunters, sell her as a dressage horse. Buy something that's either bred to jump, so you have less of a gamble, or something that already jumps well.
No horse can jump like a hunter from that dressage frame that you see her in in the video. From the evidence there you have no ability to adjust her in a way that lets her still use herself. I'd want to completely redo the flatwork on this one before aiming it at a jump.
Your mare needs to learn how to lift her back on the flat while reaching down for the bit..not up like a dressage horse.
She needs to go to the end of her stride at all gaits while she lifts her back and reaches down. Then she needs to coil up and shorten but still reach down.
A great exercise for teaching her how to use herself is to put four crossrails or very low verticals in a circle. Make sure she gets released everytime. She needs confidence to lift her back and reach over the jump. More height is not the answer with these types.
The circle exercise is hard work so be careful as she is super young. She most likely will need her canter manufactued before each jump school to help her jump her best. These horses can be taught to jump well enough over 3' but more is not likely in my experience.