I wonder is she meant she would arrange for you to be seated next to each other. The way SQ do it (to my understanding and experience), is when the flight goes to Airport control (circa 72 hour point I think) someone manually goes through any requests etc and assign seats.

They do of course take notice of status so as a *G I would be in no doubt you will of course be seated next to your wife, you should also hopefully find yourself in one one of the more foreward seats.