Hi, Kimberly!
I currently have this same situation for an upcoming vacation. A pal is staying with me, but just for one night of my itinerary. I called and a friendly Cast Member told me exactly what to do....
Book your reservation for the party that intends to spend the entire vacation with you. Everyone on this reservation must have the same plan/entitlements. When your friend arrives, go to the front desk and explain that your guest is simply bunking with you for a night or two. She can be added to your room as a guest of the resort, but will not get the same
Disney Dining Plan credits that you will have from your reservation. Remember that there is a maximum number of guests per room, and that when more than 2 adults, there may be an additional charge.
If planning any table service dining when your extra guest is there, make sure to include her in your total when making your
Dining Reservations. Your pal can simply pay out of pocket for her meals while you use your Disney Dining Plan credits.
I am so glad you will have a visitor. The more the merrier when visiting
Walt Disney World. Enjoy!
Cathy