I would say you need to learn to collect your horse using your seat and body rather than the bit. Your horse won't learn anything except to lean on your hands and no one finds it enjoyable to have to hold their horse up while riding them! I also think the horse needs to get in shape before the type of consistency you are expecting becomes possible. A horse that is even slightly out of shape won't have the correct muscle strength to hold herself in a collected state for long. I would do a lot of short spurts trying to hold the collection together and gradually increase them.