I am not sure this would be MSK related if it is coming from the vagina.
We often have blood coming through the urethra etc. can be from the stones moving around in the kidney or a stones in the ureter. If she is sure it is not coming from the cervix, I would not worry too much,. Could even be a small cyst etc. in the vagina.
Do you have any pain?
Did it appear after intercourse? Sometimes it is hard to tell where the blood is coming from as a women, but the could do a urine test with a catheterized urine to see if it is urological too. I would however encourage you to decrease activity and rest a few days. Also increase your fluids esp. water dehydration can increase the risk of miscarrage. I actually had so much bleeding with one of our sons I thought I had a cycle and was off on my dates. We actually think, as often happens a miscarried a twin. I learned recently that many women miscarry a twin early on only to go on to have a normal single birth later!
Take it easy and keep us posted!