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.