Another thought could be that your horse isn't cut out for western pleasure.
Also working on her long trot will help improve both her lope and her jog. It builds strength.
There are no shortcuts, nothing that is going to speed up the process. Take a look at my youtube videos of the palomino. YouTube - saravan99's Channel
If you look back far enough, there is a video that goes back to last summer (2007), then another clip from Jan 2008, and another one from April 2008, and then several from shows in June & July 2008. These all show the progression of a horse learning to lope & carry himself properly. The 2007 video shows us trying to take shortcuts by using draw reins and going to a full bridle too soon. The Jan 2008 video has us going back to the beginning to teach the lope the correct way - with forward motion. In the April 2008 videos we are still working on driving the horse forward. Finally in June you can see things start to come together at the shows. Right now - after six months of additional training on the lope - he is even better. This is nearly a year after we first started to re-teach the lope correctly.