What Causes Nosebleed In A 2 Year Old?

My two year old daughter had a nosebleed the other night. My wife stated that the nosebleed gave off a fowl odor. My daughter has no fever or any flu like symptoms and appears to be doing well. She occasionally has nose bleeds, but the humidifier appears to have stopped them until two nights ago. Any thoughts on the foul smelling nose bleed?
Thank you,
Eric