It's probably a Christmas card; probably from a not-close relative on Sir John's side. But here we go again: I'm Dame Eleanor, not Lady Hull, definitely not Lady John Hull, a form of address reserved, I believe, for old-fashioned wives of dukes' younger sons (as in Harriet Vane becoming Lady Peter, for social purposes, when she married).
And since this is the USA, the social niceties aren't nearly as tricky as working out who's who among British aristocrats. How hard is it to ask people who marry what they want to be called? She might or might not change her name. Sometimes he takes hers! They might hyphenate, or adopt a name meaningful to them both, or combine.
Combination actually makes for an excellent party game. Which guests ought to get together just for the name possibilities? Dart and Staley become the Dastardleys! Villalobos and Barton become the Villains! Who ought to eschew any such partnership, or, should it develop, avoid name-combination at all costs? I can think of some well-known scholarly collaborators who, at least for nomenclatory purposes, should keep their collaborations to the intellectual realm.
Well, yes, I go to some very nerdy parties. But we nerds have fun, too, in our own weird way.