[It was indeed Constance who was on shift when the Charmings asked about the possibility of having larger rooms and more space (or perhaps more accurately, was on shift at least one time when they did), and so when the house appears, Constance wants to see it for herself.
Except as happy as she is to see them having an entire house that they can now live in... seeing the domestic bliss, watching them fix up a house together with their family and friends, well, it serves as a rather acute reminder of the state of her own marriage back home. This is how marriages should be like... and yet for her and nearly everyone she knows (she can't help but think of the queen, too) back home, it isn't like this at all.
So instead of going to congratulate Snow, or approaching to help out, she'll stand close by, looking at the happenings with a wistful expression, obviously lost in thought.]