My girlfriend started bleeding in her mouth after a nose bleed, it's been 24 hours and it hasn't stopped. why is this happening?

Need ED: You need to go to the ED. Severe bleeding from the nose or posterior bleeding goes to the back of the throat. They will pack the nose for her. They are generally vessels on the septum, but after all is good will need to be checked by ENT to look in the nose and make sure there is nothing else in there causing the bleed other than the vessels such as lesions .