Now or at checkin is fine. I always do this is my mom decide to visit while we are there. She'll book a different room elsewhere so the kids don't jump on her 24/7. I'll sign her up as a 5th in our room for concierge and she can visit and enjoy the guest status there as well.
<b>Actually, you are entitled to four people per room with no further charge.</b>
If I were you, I'd simply include her name for security purposes, but you should NOT incur any further charges.
It depends on which hotel you have a standard room is that will determine the most readily availabe configuration. You didn't mention the hotel, but you can always call Disney and ask or look at <a href="http://www.wdwig.com">Deb's site </a> for the layout if you don't find them here.
The Polynesian almost always has the sofa bed as does many other rooms but I don't know.
You can call in for a specific room request 10 days in advance of your arrival before they put together who gets what room at the resort.
I should like to add that your concern for being honest and accountable is a resfreshing start to my morning. Generally everyone I run across the boards here is a "stand up" person which is why I return so much. I hope you have a wonderful, safe trip!
