Possibly a nose bleed - but this is not a forum to replace medical care, get her to the ER ASAP it could be serious. This happened to me at age 12 at summer camp, during my sleep and my mouth filled with blood, all over my pillow, and my nose bled, and it was determined by the local hick doctor that he couldnu2019t figure it out. I had a ruptured blood vessel in my nose when I sneezed in my sleep - specialists said months later. That next year I had rheumatic fever which changed the course of my life putting me on steroids, antibiotics, and a half year of bedrest, with no exercise for several years. GET HER TO AN ER