Here, to save time:
MK
Goofy's Barnstormer - 35 inches
Big Thunder MTN - 40 inches
Splash Mtn - 40 inches
Space Mtn - 44 inches
(Stitches great escape) I believe I saw this - 40 inches
The Speedway Cars - 50 something inches to drive it, any size just to ride it.
EPCOT
Body Wars (if open) - 40 inches
Mission Space - 44 inches
Test Track - 40 inches
MGM
Tower of Terror - 40 inches
Rock n Roller Coaster - 48 inches
Star Tours - 40 inches (if it's not too busy, the might allow a less turbulent show for smaller children - try asking when you get there)
AK
Kali River Rapids - 38 inches
Expedition Everest - 44 inches
Primevil Whirl - 48 inches
Dinosaur - 40 inches
I believe these are all correct, but if not, I'm sure somebody else will let us know
I understand what your friend is going through. When we go next year, my daughter will be 7, and just barely topping (we hope) 40 inches. There's nothing wrong with her, she's just very short (my wife is all of 4 feet 10 inches), but I know she will not like that her brother (10 years old) is tall enough for all the rides, and she isn't.