Petsflowers, I have nothing against Crete, in fact I love it madly. It is simply that to me, sounds like SO much time on your trip plan will be spent simply on travel. You want to do Everything in 3-4 different directions -- NE to Meteora, N to Delphi, and waaay S to Crete and W to Nafplio. This is especially challenging since your trip will be during almost the shortest month of the year, when it gets dark before 6 pm (unlike june when you have THREE more hours to travel and/or sightsee). Not to mention the short winter hours, closures at 3pm. You have 16 days (not counting departure day, or arrival day unless u arrive before 10 am). If you did the list i roughed out From Athens thru Nafplio = 11+ days IF all goes well ... then you have 4-5 days to Fly to Crete (Chania) , rent a car? drive around? fly back from Heraklion the night before homebound flight. So yes, you could do it, that's if everything goes smoothly. If you want to try this, be sure that each place is somewhere you really want to see.
What makes something an absolute "must-see" for someone? Because they are SO drawn to a dramatic landscape? or have an affinity for religious destinations like churches & monasteries? or they're steeped in Classical studies and thrill to ruins, sculptures and archeology museums (that's my case). Some items are on a list because they are supposed to be Famous, or a friend said it's a must. That's not always right for everyone -- that's why it's important to do some research yourself; to look at some comprehensive guide books? Yes I know they are old-fashioned but they often help people choose what THEY want most, based on more knowledge .
Example: Is Crete what your daughter reallly had in mind for "at least one Greek Island?" Maybe she envisions the famous "postcard views" of snowy white buildings, blue shutters and red flowers, on a cliff overlooking the sea? In that case, you need a Cycladic island. That's not Crete. Its best-known Old Town, Chania (and many of its villages ), are golden stone with terra-cotta tiled roofs, looking more like italy. What's more, Crete is so big it doesn't have an island "Feel"... any more than one feels "islandy" on Long Island NY. Of course Crete has many swell things beyond "white-cube" houses ... huge mountains, gorges, ancient ruins, lovely harbors and fortresses, country lanes, wonderful small villages. But it's hard to see much of Crete -- it's really a country -- in less than 5+ days, even then really need a car, & well- organized plan, If you don't want to drive, then u'd better stick to the North Coast's 3 main towns.
Find out what island your daughter really envisions. (1) If Crete is it, to simplify things I'd advise you, on coming back from Nafplio, to go straight to Airport, Fly to CHANIA, spend 2 days, Then Bus to Rethymnon, spend 1 night (it has a University, so more youth-action). Bus to Heraklion (IF you want to see Knossos). Fly back from Heraklion & spend final night near airport. (2) If she wants an island with that "white cube" Cycladic look, only a few have permanent year-round Populations. You might fly to NAXOS, and stay in the Port Town (Hotel Grotta is scenic, just up a hill from the ferry). Stay 3 days -- you may be able to get a bus tour that goes around the island. Explore the interesting port town; enjoy dinner in the local tavernas, with the Naxians (they love to eat out, year-round). There's 1 flight back on the 29th.
Main thing: your destinations should be because YOU both want them, not because Somebody Said. Realize that when you want to see a lot of widely-separated places in a limited time, you're going to spend $$$ on transport. Build-in realistic time for travellng; it's the Big challenge in Greece. (It would help to have a magic carpet, or Star-Trek teleporting skills -- "beam me up Scotty"). Good luck and have fun!