Get some better photos! You need one good ridden flatwork photo to show her paces, and one good jumping photo - preferably over something like a spread with a filler.
Rather than saying excellent dressage/jumping prospect, why not say (if it's true) that she has nice flat work is like and jumps well. Say a little bit about what she's done etc.
Unfortunatly i dont think it has anything to do with your advert, I think it is more to do with economic climate at the moment. I know of several people with adverts running at the moment, and they are all saying the same, just not getting the calls, hope things pick up for you.