Well, I already have to eat my words on one point: I do have an example of the heart-shaped, wired "frame" cap from the correct period. The miniaturist Isaac Oliver painted a portrait of his wife wearing one in about 1610-15. Of course, since he painted it, she's clearly not a widow; and she's not wearing any veil, just the cap. Hers is wider and not as tall as the one in the painting under discussion, but it *is* set as far back on her head -- the tips just touch her earlobes.