Many years ago when I first heard of a BVM statue weeping tears of blood, my
first reaction was to say it must be a fake. Then, over the years, I gradually came
to realize that if tears of water, that is, human tears, would not be impossible for
a statue to shed, like the wooden statue in Akita, Japan in the 70's, and since then
the state of the world has without question gotten much worse, then why would
blood for tears be impossible? After all, the sweat of Jesus in the Garden of Olives
became drops of blood, and this is medically possible under the most severe stress
and anguish.
If Our Lady is trying to get our attention, what other thing could she do?
The miracle of the sun in Fatima was not sufficient for most people since then.
As for blood type, it's true that people do not change blood type in this life, but we
are not really talking about this life, when we refer to Our Lady. She is in the next
life, and we don't know much about that, do we?