Thelma's place is a great place to stay if you would like to get the feel of a typical apartment in Athens. It is close to the metro, which makes the rest of the city accessible. The apartment is also safe, clean, and has all the facilities Thelma mentions in her write up.
Do make sure you have the map to her apartment though before you leave, as streets in a big city can be confusing. Thelma usually sends the map out to guests before they arrive, and it's a reliable guide to get to her apartment.