The true key lies in something you have not discussed - the reasons for your friend's preference(s). I'm assuming it's a she... what does she want to get from Delos/Mykonos? Is she a classics buff? If so, and has studied up on Delos, she'll get a lot, otherwise it will be just a bunch of tumbledown stones... compared to other Greek landmark ruins, as Gertrude Stein would say, "there's no there, there." And as for Mykonos, does she want to see the white & blue harbor town? (NOTE: Naxos v. similar, minus the high-end Luxe shops like Cartier, Hermes etc) .. the beaches? (same kinda sand as Naxos, sunbrellas & sunbeds cost €18 vs €7) ... or is it primarily the fabled nightlife (mainly in July-August -- in Sept., usually after midnight). I note that you're coming from Party Central, Capri, so maybe nightlife is the attraction.
If it's mainly the harbor-town look, you can easily get it in the Wednesday day-trip on MV Alexander (and BTW, if on that day-trip you'd wish to skip Delos, u could stay on vessel while Delos-lovers get off, then go straight to Mykonos about 11 am). However, if your friend's interest is mainly in Mykonos partying, a day trip would not do. (In that case I would warn against booking a room anyplace but in town -- Busses stop about 11, mykonos taxis disappear at midnight or so & people wanting to reach beach hotels are stranded)
I can see that you did delete Santorini to save more time for Naxos, so you would still be able to explore the island (NOTE: in your new plan, on first Naxos day, just concentrate on exploring Naxos town - Causewy, ruins, castle, fascinating winding lanes, museum, shops, harborfront sunset. U can rent a car for day #2 then decide about day #3).
Also, your original thread seemed to have at least a modicum of concern about budget (AirBnb, "cheap-ish" flight). How does that square w. €18 to lie on a beach, or €20 Mykonos club drinks? Why the change of tune? I do see you have some remaining budget concern snce you cite that 2:30 pm flight -- I'm guessing mainly because the "GoLight" fare is €96 vs €117. You need to read the fine print; "go Light" does not allow a checked bag, only a small carry-on personal bag. Checking your Rollaboard will cost you at least €25 wiping out any savings. If u decided you could party in Athens instead, you could take the NISSOS MYKONOS ferry Saturday at 19:35 (7:35) -- a big ferry, (about €38 for reserved seat), open decks to sit out, lots of cafes & bars aboard for socializing -- it would arrive Piraeus at 11:35 pm, you could get the Green line Ferry (30 minutes, €1.8) to a Central Athens hotel by 12:30 and then go hit an Athens clubs -- on weekends, they're jumping until at least 3 am.
Of course it's your trip, not ours, do whatever you like, I did my best to try to help achieve your original wish list; done now.