That's not a whole heck of a lot of money. Sounds like one of them rented out their townhouse or apartment after they got married and bought a house for both of them. And at $1250 per month, it's probably not in big-ticket DC. The taxes on it would be up to $3000 in addition to insurance, possible HOA fees and upkeep.
Not excusing the hypocrisy, but haven't they got bigger fish to fry?
She owns a two family house. She rents out on floor. Very common in Boston.