Holy long back, Batman!! My horse is long but that's just insane. I also see a weak loin and she looks a little herring-gutted... not underweight as such just needs muscle and is built sort of like a greyhound (not a good thing in a horse, limits heart and lung capacity, but she'd be fine for most things... just maybe not eventing and other such highly strenuous activities).
Other than those three things though I really quite like her. Lovely shoulder, nice hindquarter, neck fits the rest of her. I like a chunky, archy neck, so her neck is not for me, but it's not a bad neck... just not to my taste. Nice face, neck ties in a touch low but that's a paint thing. She is quite likely at least a little bit downhill in build, but you're right that ground does not look level, so it will not be flattering her.
She's a year younger than my boy :)