On the 21st start the day off at Chef Mickey's for a character breakfast. This is at the contemporary resort and you need to get a Priority Seating!!
Tell the hostess/host that it is her bday. We did this a couple of years ago for DS and DH bday and this is what Chef Mickey's did: both received the "Birthday" button pin, placemats, cupcakes after b'fast, they sang happy bday, and I think got an extra visit from mickey and minnie for another photo op. When you go into MK after this, all the CM's will see the button and some may give her trading pins

(this happened w/ my ds) , they will all say happy bday and she will feel so special!
Another cool thing to do at MK is to go to the barber shop on main street and have her hair fixed. Even if they don't cut it they can do it up and put "pixie" dust in it. We have yet to do this but I really want to. I think this runs about $15 (usually for a cut and do).
Of course there are always the fireworks at night and at fort wilderness (FW) you can see the FREE campfire program and disney movie. Not sure on the starting time probably 8pm since it gets dark later now.
Also, the easiest way to travel from FW to MK is by the boat. You should probably post another thread on the family board to see if anyone has any suggestions.