I know that if you are all staying in the same room, you all go to the same check in. If you are in different rooms that might be different.
However, if so far she is booked into a room by herself and you have a family of more than two in your stateroom, it might make sense to book one person from your family into her room. As a solo traveller she will be charged nearly the full cabin fare for two adults (just not the taxes), so by moving one person out of your cabin, you all will be able to save money. As far as I know Disney does not really care who sleeps where. And if one of you Silver CC Members is in the cabin with her, that cabin qualifies as a Silver cabin with all the earlier check-in and port adventure booking and the Check-in at the port.