Yes it certainly can be from a STD.
bloody show...though it may not be "bloody"
Yes
No, mucus in the vagina is normal and is sometimes a sign of increased fertility
Not sure about your question, but mucus is a normal thing for the vagina. The tissue in the vaginal sheath contains goblet cells that secrete mucus. This is completely normal and helps to prevent tissue damage. If the vagina did not stay moist, that would be completely unhealthy and require treatment to prevent permanent damage.
no No, it's vaginal fluids. Not always, it could be ejaculate or some other vaginal mucus.
Something is wrong, it could be an infective, inflammatory, autoimmune or benign or malignant neoplastic problem . You need to see a doctor as soon as possible.
Mucus in the stools before a period could signal a condition such as irritable bowel syndrome. It may also be hormone related.
I am 52 and have undergone menopause, without any touching, when I get aroused there is blood in my natural vaginal lubrication. When your bartholin's glands (located slightly posterior and to the left and right of the opening of the vagina) are not well aroused, they could fail to produce the mucus which is intended to make your vagina wet which could cause friction that can lead to the bleeding. Or as above, some women's vaginal lubrication tends to be bloody at times although if it has never happened before its better to get checked by your specialist.
not that i know of, i recommend seeing a doctor for it right away.
It is possible that she is ovulating ("in heat")
It is possible to dilate without bloody show or losing your mucus plug.
This residue that you are speaking of is most likely the mucus that keeps your rectum lubricated when you have a bowel movement. Having a little mucus drip onto your underwear is normal, but contact your doctor if the mucus turns bloody.