Greece is the safest country in Europe, Athens the safest city and women should not be worried about traveling alone. Chances are also good you will meet someone else who is also traveling alone. As for terrorism there is more of a chance that you will drown or have a heart attack in the shower than be killed by a terrorist. Not that the showers are dangerous either.

Most people you will come in contact with will speak English since most people you come in contact with will be waiters, hotel employees, travel agents, shop owners and people involved in the tourist trade. But even in non-touristy places the number of people who speak English is remarkable.