We had a very nice stay at Lucy's who is a great host.
She was very available and gave us valuable advices.
The flat is quite big, very clean, and we had a bathroom just for us.
From Stansted airport, the bus (national express) stops near the flat. The metro as well is very close, and with District Line it's easy to reach the center of London. We also tried the bike (Santander bikes), there are bike lines everywhere, you can easily go anywhere.