What about schooling her in a different enviroment. Like, if you school everyday, do one day in the chool, next day in a feild or hacking. You can keep her intrested if you are constantly changing enviroments.
I would even say half and hour - forty minutes (or less) in the school and then an active hack would keep her intrested. Try setting out poles in different formations, or playing games once a week. If all you do is school, she may begin to bore easily.
Keep her intrested! Change is the key.
Try riding with another horse once or twice a week if possible, and maybe do games (such as classic gymkhana games) and maybe even beginner dressage tests.
So school hard twice or three times a week, hack once or twice and play games and CHANGE ENVIROMENT!
Riding with another horse can really keep their attention (but I don't know, maybe it will distract her more). But this may not be possible.
If your horse says no, you either asked the wrong question, or asked the question wrong.* ~Pat Parelli