Most likely there was a Helen of Troy, since there is good reason to think that the basic facts about the Trojan War described in the Iliad and the Odyssey are historical. You could fiddle with the minor figures, but figures like Agamemnon, Menelaos, and Helen are unlikely to have been sheer inventions.
The Achaeans were newcomers to Greece at the time of the war, who conquered and ruled over the Greeks who had lived their earlier. The usual theory is that they came down from the north. Achilles and Odysseus are both described as red-haired or blond, and so is Menelaos. Fair hair may have been fairly common among the kings and nobles of that time.
I don't see any reason to believe that this particular woman was Helen, though, and not some other noble or royal lady. It's sheer speculation, a good way to get on TV and sell books.
I agree, the outline of the story is most likely true and the story's main character most likely real, with a good deal of literary license of course.
Also the Spartan (Doric) women were known to be the most beautiful in Greece which I always thought of as a waste. It may have been partly due to their eugenics practices.