Tagging in @armiyana, @akmorphs, & @ballornothing for you, since I don’t work with BPs. That said, to me it looks like a case of cloacitis, and may require antibiotics to clear up, especially if she’s gone off food.
I agree with @noodlehaus on the need for a vet and most likely antibiotics. But I would also have her checked for parasites as well.
This is fairly similar to how a boy of mine looked on a positive parasite test. If she poops I would try to get it in a ziplock baggie and put it in the fridge to keep it fresher so a vet can run it.
Definitely a vet visit is in order. That looks painful to me……
You’ll need to go to a Veterinarian for this.
I’d agree with the others on going to the vet.
If you have gnats or phorid flies in your house make sure you keep the cage clean and don’t let any get on the snake. I’ve had them lay eggs in a wound around the vent and then the maggots become a big issues once they hatch.