Try a different feed with higher fat
oats + molasses and get her off the pattern for a lil while.. go for a few trail ride
Sometimes if your horse is lazy they are lacking in feed such as minerals or electrolytes. Maybe try to figure out if your horses needs are getting met with there grain and forage.
When you are hacking/lessoning make up games to have fun, doing the same thing over and over again can get boring... you can literally make up any games and she will have fun, anything new will spark her interest