Hurray for you, Jackie! If your mom managed OK in Venice, she can manage in Greece, with some of the precautions already noted. I've visited Greece 12 times since '99, never get enough, tho now past 80 (good health & lucky genes) On 9 trips I've taken along 3-4 "Newbies" so have made multiple trips uphill to landmarks, so can speak from experience (BTW, it helps us if you say exactly when you'll come. Advice differs markedly for trips in May/June (my pref) and July/August (hot-crowded-tiring-costly). And does "9 days on the ground" mean you are coming to Greece from Elsewhere in Europe? That can affect what time of day u arrive at ATH airport, which can also alter our advice.
MY SUPER TIP for ELDERKNEES !! -- Go on Amazon for Earthtrek Folding Hiking Trekking Pole (Shorter version). Just for women! adjustable 38" - 42.5". VERY Lightweight, strong, 5 segments, folds instantly down to under 12", fits into a daybag. $27. I got 2, loooove them, takes ALL the stress out of climbs or pathways, hikes --- these transformed my 2015 trip!
Possible sequence: 3-4 days Argolid, 3 days Athens, 2-3 days an Island.
ARGOLID AREA -- Since there are so many sights (AND fine beaches) in this Pelopponese area so accessible to Athens, I highly recommend spending at least 3-4 days there. For efficient use of your time, I would suggest doing this on arrival. If your plane arrives 9 or 10 in AM, head straight there; if in afternoon, I can suggest a B & B (with pool) by airport where you can get over jet lage and then travel next AM. You'd have the option of Car rental @airport/return it there ... OR take a KTEL intercity bus (2.5 hrs, €13 one-way, reserved comfy seats). Then just rent a car 1-2 days IN Nafplio for sightseeing outside town. Comments:
NAFPLIO Old town -- gorgeous, very flat. If you're renting a car, you can drive it UP a ramp drive to a high parking square where, there's an elevator right in the rock cliff (Yes!!), takes you up to the Acronafplia ramparts. With a car or taxi, can also DRIVE up the back way to PALAMIDI, for its stunning views. DONT MISS the small superb archeological museum, AND Folk Museum. Ippolito a good hotel also look at Omorfo Poli.. For Swims, 10 minute drive or local-bus ride outside town is TOLO resort village, sandy beach, the "feel" of an island. In fact, Nafplio itself, on peninsula, feels like an island.. As for area sights:
• MYCENAE -- Frankly a LOT of steep climbing; has a museum, but its great treasures are in the Nat. Arch. Museum in Athen
• TIRYNS - an easier option 5 mins outside Nafplio another massive Iliad-era fortress, much less climbing, no crowds.
• EPIDAURUS - Just stick to the theatre, not much walking/climbing -- and you'll never see a more thrilling ancient arena!!
ATHENS -- Key tip: stay CLOSE to Acropolis, minimize walking & when u get tired, you'll be close to your hotel. Schedule a NAP! SOUTH side of Acropolis, mostly no-car lanes, with a lovely promenade. 3 good hotels near Acrop entrance, AND Museum: Airotel Parthenon, Hotel Phillipos, Hotel Herodion. Your mom WILL have to climb up to Acrop but it is Do-able.
If an island is a MUST, you can get to a nearby island, Aegina, 1 hour from Piraeus harbor (go weekdays, Athenians crowd it up on weekends). Nice port town, a stunning temple mid-island, a couple of good beaches, w. hotels for a 1 night stay. Others have suggested my favorite Island NAXOS and it's possible, but would require tight scheduling: fly on arrival (1 flight per day), and either fly back or 5+ hour ferry trip. You need to tell us more, so we don't toil away at scenarios that prove inappropriate.