I doubt Diana's putative virginity was a consideration, all the Royal Family needed to know was that she wasn't pregnant by someone else!
What was worrying was the fact that the heir to the Throne was over 30 and still unmarried and showing no inclination to marry.
Obviously, if he had married a woman of his own age, there would have been concerns that she might have difficulty conceiving, but he could well have married a woman in her mid-twenties without that being a bother.
Why anyone ever thought a over-sensitive nineteen year old from a broken home a suitable bride for any member of the House of Windsor beats me, and did then.