Hi mannipatch,
I am Greek, I am not from Agios Nikolaos but I'll try to help you.
Agios Nikolaos is a small town, and most locals in small towns do their nails in a hairdresser salon or use mobile techs. A salon exclusively for nails rarely exists as there is no profit only for nails in small towns.
There is another area near Agios Nikolaos (11 km), called Elounda which has the luxury hotels with the spas (I believe moopie was referring to that area).
I did a google search for hotels in Elounda and services and from what I saw, they offer services for natural nails (spa manicure and pedicure). I did a search in a hurry so probably there are hotels that offer nail extensions but that area is very touristic and they are pretty expensive. Most of them have sites of their own and in English and you can also have a search.
If she is married to a local, she can surely ask his relatives where they have their nails done. She can take a lot of info by them.
Another idea is her hairdresser. Who is going to make her hair? If she is local she surely knows some techs.
If she is just married there, and if she goes earlier, since it's a small town, she can have a look around for hairdressing salons that offer nails services, or even a nail salon.
Mind though that as moppie said, the products they use and their techniques are questionable. They may have top quality brands but they may have not (I am talking about local hairdresser salons, not the big spa hotels)
Also about e-files...It's not illegal in Greece and techs can use them freely, either trained or not. The majority uses them mostly for cleaning up cuticles and for infills or complete removal of the gel/acrylic.
I hope I helped you a little. :hug: