It had not occurred to me either that Elizabeth might not be doing enough by way of mourning. Your point about "weepers" being white convinces me that Elizabeth was the one wearing the black ribbons.

What a puzzle it all is. I find it instructive to realise how much information about such commonplace topics has been lost in less than two centuries. I'm sure that when Persuasion was first published, readers would have been able to make a much more nuanced interpretation of those black ribbons.