Yeah, get the skin so soft, pour a bit in your hand and wipe it over the crest if the neck, root if the tail and her underside. Don't rub it in, just superficial, but generously. It's oily, so the gnats can't bite through and the smell (pleasant to us) keeps them away. Twice a day will be necessary, gnats fly dusk and dawn. Maybe keep her in until 9am, do her then and do her again around 5pm.
Try to get this prozap thing for in her stall, it does work!
Another thing, and I suggested some serious training on this, remember
....cut the weeds and long grass. That's where the bugs stay. And keep stall and paddock clean, too.