Are there wounds on the neck or breast? Or is it blood from the mouth? Head/eye/tongue wounds can bleed a lot (think nose bleed!) and a little blood makes a big mess. Check the tongue, skin under the feathers, nostrils for dried blood. Wounds to the skin suggest rodents. No wounds but blood in mouth/tongue/nostrils suggests head trauma, possible head bonk, caught her tongue on a loose wire…also inspect the cage for blood spots and hazards.