My 78 year old great-aunt and her 70 year old friend went with us on a family trip in 2002. Although they could both walk well with small breaks, we weren't sure what things they might like in terms of attractions. But here are a few...
MK-Small world, Peter Pan's Flight, Carosel of Progress, new now but Mickey's Philharmagic, Haunted Mansion, Pirates (DGA LOVED this one!), Country Bears, Tiki Room, Jungle Cruise (she loved this one as well), Hall of Presidents, all of the parades and shows (she can't get enough of parades)
EPCOT-A lot more to do here in terms of taking your time and strolling through the countries. Also, the rose garden is a great thing you might want to consider taking her though. My DGA loves flowers and we spent 20 min. one morning just taking a moment to "smell the roses!"
Hope this helps!