I didn't get to meet Lena.. my flight came in late so I didn't get to the apartment until 11:30pm, and she left the key at the kiosk across the street. There was some confusion when I tried to get the key, but it was due to my lack of ability to speak German (important: 'key' in german is 'schlussel'). I texted Lena and she immediately replied and luckily it all got straightened out.
As for the apartment itself.. Amazing. Such a wonderful and beautiful apartment. Very spacious (it was bigger than I thought it would be from the pictures), all new and modern appliances. It was spotlessly clean. The floor heating was the best thing I've had in all of europe. Not to mention the giant bathtub and shower. I was skeptical about the round bed at first, but it was verrryyy comfortable, and the pillows and blankets were all some very soft and warm feather things.
The area is really great as well.. lots of hip bars and restaurants.. a markethall across the street where you can get anything you could want, or just hang out and have a beer. Short walk (maybe 5 mins) to the U bahn (metro-subway).
Even though I didn't meet Lena, she was a great host and answered all my random questions about Berlin via text, and the apartment, if I haven't emphasized it enough already, was totally amazing. It was one of the most pleasant stays I've had.. I plan to come back to Berlin in a few months and when I do I will definitely look to see if Lena's place is available.