Some of her tenants, for reasons hitherto unknown, rent from her in multiple locations, most notably Nigel (who lives in her buildings in both Los Angeles and New York, and perhaps in Boston as well).
In a future she seeks to prevent in the story “Deus ex Machina” (from the collection Those Little Bastards), Henderson bears witness to the mass destruction of a city by a horrifying creature born of the collected “sin” of the city’s denizens. This future is chronicled in the short story “Revelation” (which also appears in Those Little Bastards).
According to the now-apocryphal introductory matter of the 2002 edition of Those Little Bastards, Henderson was born in 1935 in New York City as Emily Baker, married a man called Ernest Henderson in 1955, and died 13 November 2034. The same document indicates that Henderson had one child with Ernest, a daughter named Nora (who was born before 1980), as well as one unnamed child born before Nora.
But Emily Henderson’s true origins are shrouded in mystery. Unless you like spoilers.