Hi

I had a 'lazy' horse for years.

I realised late on in life I often fed him an unbalanced diet as he was a good doer, if you don't feed a full ration of cubes or mix, try a balancer to make sure she is getting all the vitamins and minerals she needs.

Also I realised that I actually taught him to ignore me as I constantly nagged with my legs and he just switched off, also my timing was off with use of the stick so it never reinforced my leg aids.  If your mare gets cross with the use of the stick, sounds like she is finding it a punisher rather than having learnt to go forward when it is used.  The austrailian equine behaviour centre have a great training methodology, check out their website as you might find something on sharpening up response to the forward aids.  

Hope this helps

make hacking and schooling exciting....trotting over trotting poles and 'playing' in the school is a good idea. Also, if posible, turn her out in the school for half an hour so it's not a 'work' place, and give her a feed. If it's sand, wash her then put her in to roll and play.

When doing the right thing, it's easy to make a lazy horse a fast horse. Hope this helps :)