That's where I'm at on it.  I would have Wife check sent items and double-verify the email address it was addressed to.  If that checks out, I would have her send about 10 separate test messages to you.  If all 10 of them come through to you, then I am baffled.  if more than 1 got replied to by this other account, then it's not an infrequent thing that's happening, just no one else has replied.  If it's that common, all 10 test messages likely aren't coming through to you and I would contact gmail about it at that time.