Marina and her son are wonderful people. You'll get detailed instructions about how to get around Oslo and how to find the place, plus tips on what to do, and they'll be ready to answer any of your questions or just talk about anything else.
The apartment is cozy and clean, and is situated in a calm residential area. Kværnerbyen is a bit secluded from the rest of the city, but reaching the centre of Oslo is quick and easy thanks to the bus service. For your everyday shopping needs, there's a Kiwi with generous opening hours just minutes away.
The room itself is tiny, no doubt about that, but there's plenty of space to both store all of your stuff and to sleep comfortably. Marina does not necessarily respond immediately because of her working hours, but she is upfront about that and you can rest assured that she will get back to you and deal with any of your needs!
I had a great time!