Turns out the maid of honor's name is Bernie.
So I ended up being Surrogate Bernie, and helped them choose stationary, discussed the pros and cons of different reception halls and the politics of extended family (she's Catholic, and apparently her parents were insistent on inviting all the distant cousins, such that if they went with the 300 seat reception hall, she wouldn't be able to invite any of her friends). I told her that her close friends are her chosen family, the family that her family don't recognize. Her mother-in-law and I both reminded her that she is perfectly within her rights to strike the "and obey" from the vows.
"I can do that?"
Yes. People write their own vows all the time. And any priest who'd insist on keeping that in wouldn't be officiating a wedding with an Episcopalian anyway.
Kate looked relieved.