"You and Kim will end up in your own ‘Grey Gardens’ one day,” a friend’s boyfriend whispered to me at a party a few years ago. The “Kim” in question was, of course, my mother. At the time, I hadn’t watched the famed Maysles brothers documentary, but I was familiar with the gist of it: a mother and daughter, both single and unemployed, live together in a microcosm of their own at an eccentric estate,…