My friend and I stayed in Linn's apartment twice: once for two nights after arriving in Oslo, and one extra night preceding our departure.
The apartment is perfect and has a great cozy vibe despite its large size. It's also very well connected to the downtown touristy areas, and a short walk to Grunerløkka.
Line was easy to communicate with and very helpful prior to our arrival in Oslo. The apartment was stocked with tea and Line provided us with a map, guidebooks and info on using the public transport. I'd highly recommend her apartment for your stay in Oslo.