Question for the easy stuff... have you fed any berries, beets or fruit/veggie that has any reddish color at all? Birds love beets, but it looks like a crime scene by the time they are done...
Then thoughts / questions more worrisome...
Regurge and blood could give that look. Check the paper on the bottom of her cage closely and wipe down the grate with a light colored rag, look closely for any other indication of blood or that reddish colored discharge.
Don't panic, but also look at toys, make sure there is no indication that an injury to the tongue or inside of mouth could have occurred. We had something similar happen at the shelter and of course rushed the bird in to the vet, had full bloodwork and everything done only to come to the conclusion tearing apart the cage that the injury was likely related to shredding wood and much like people poke themselves with a straw or toothpick, she stuck herself with a piece of wood shred.
But agree with Printer Bird... pics of what food is in the cage and offered daily. Hot peppers in the mix? Do you feed zupreem or pretty bird colored pellets?