It looks like 3 cuts to me.
If this were my horse, I would shave down the area so that no long hair touches the wound. Irritation from hair will impede healing.
I would clean it with a mild soap and water solution, like Dawn dishsoap. Rinse it really good.
Then I'd mix sugar and iodine together to form a paste, and smear it on really good.
The more times a day you can wash and paste it the faster it will heal. If she is out on grassy pasture you could probably let it stay open. If she is in a dirt arena or drylot I would bandage it. I'd use a moist bandage though with the sugar/iodine solution.
Spent a whole hour today laying in a pasture, waiting for a sparkling vampire to show up. Alas, I woke up and looked over, only to find a mound of horse crap. Sigh.