Your BO is not a vet. Period.... I am so amazed at how many horse owners look to their BO or trainer as a vet.. They are not vets. Their advice could kill someones horse one day, as I am sure many times advice has killed horses because the owner thinks the BO or trainer is a vet or God or both.
I have worked for vets for more years than I care to count, and I have seen endless results for "home vet care" because of not wanting to call a vet out. Some die, some have massive infections, some recover some don't. All because somebody can't afford the vet or the BO or Trainer or next door neighbor or whomever says" its not a big deal".
Don't treat open wounds with salt. Not a wound on the head that could be in sinuses for sure. Get the vet out. Can't tell you the number of times I would be out in field with the vet on emergency calls on holidays. Just the way it is
If you can't afford emergency vet care when it is needed, then you need to think about saving money for it. I realize you are a teenager, but your parents should be aware that horses cost money, they do not save it for good days, and that the BO is NOT a vet. I can guarantee the BO will not pay for the vet care, that is your responsibility. She did not injure your horse, your horse injured itself.
At the very least, this horse should have been started on antibiotics yesterday when this happened. Infection could already be started, and if you wait another day, just more chance of issues.
Get the vet out.