As team fire said, very few horses have the conformation for upper level Dressage, and this one is no exception. She'll be fine to do some lower levels on, but don't expect anything amazing.
I know that people cry breed snobbery over this, but there are specific European warmblood lines that have been developed over centuries towards Grand Prix potential, which must be an appropriate mix of conformation, paces, temperament and soundness. Of the thousands of extremely well bred warmblood foals that hit the ground each year, maybe a handful will be suited to upper level work.
The chance of picking one of these horses put of a perch x Arab is extraordinarily slim.
However, as you are only riding at first level presently, I don't think you need to be looking so much at an upper level prospect. Find something with 3 good paces, that naturally swings it's back and sits on its haunches, and has a willing temperament. If it can get you to medium/adv then it is a bloody good horse.
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