I had planned on mentioning this as an option, although I highly doubt my friend will go for it. She'll still be breastfeeding, won't want to be away from the baby that long, etc.
When I spoke with Disney I asked "Am I correct in thinking that everyone staying in that room must be booked under the same package? Meaning that everyone has to purchase the same dining plan upgrade and the same number of park tickets, even though Grandma has no intention of using any of them?" The woman who was helping me replied with "That's correct". But you were told you could get around that by just showing up with Grandma in tow and adding her to the room at check-in? I don't understand why Disney would handle it that way. It seems like it should be either everyone has to be included on the package or they don't. I'm not sure why different rules would apply depending on when people are added to the reservation. I guess I'll have to call Disney again, but now I'm not sure how I'll know if the person assisting me is giving me the correct info, seeing as how people seem to be giving different answers.