סיפור אבישג השונמית – טמפ' גוף

This is the question:

At the beginning of Sefer Melachim is the story of Avishag Hashunamit.

She lay with David Hamelech to keep him warm. She was a betula and is also described as yafa. Rashi and Metzudat David (verse 2) explain that a betula's blood keeps her warm and in
verse 4 they say that a beula does not warm as much as a betula.

(1)What is the difference between a betula and a beula with regard to the above?
(2)Is this consistent with our understanding of medicine today?
In verse 3 Metzudat David explains the significance of "yafa" that beauty shows an abundance of blood which results in more warmth. (3) What is meant by the term "yafa" and how does it affect one's blood?