I would put a rubber band (white) in her forelock. Practice either putting all of her forelock in one or dividing her forelock in half, upper and lower. Put a rubber band in the top half, about halfway down, then bring it down straight and put a rubber band around the top portion and the bottom portion you set aside. Does this make since? Her head does not look too big, she's just loosing her facial muscle tone with age. I would also trim out her ears and clip along the outside, following the ear around, get rid of the fluffies.
Maybe practice with someone else observing different levels of her holding her neck/head. I think if she had her head a little higher than it is in the pic, not straight up, but just a little more raised, she wouldn't appear droopy.
Does she like pepper mints? If not then you could use pieces of carrot or apple, but use the crinkly paper from a mint to signal to her that she is going to get a piece of carrot, her ears should come up - alert, then give her the treat. Do this several times, then just crinkle the wrapper and when she puts her ears up just give her a good pet and tell her she's a good girl. So, when you are in the ring and the judge comes by to look at her, the big one last glance at your horse profile look, crinkle the wrapper and she will have a very pleasant animated look, but no petting or treats in the arena. My horse falls asleep in halter, we need this trick to pull it off. Here's a pic of her from our last show.