Definitely stay in Marianna's apartment. You won't regret it! In the past, I've both lived in Rio and visited many times and this apartment is the nicest, and by far, best value of any place we've ever stayed.
In recent years, I was always hesitant to stay in Lagoa when coming to visit, trying to stay closer to the beach to maximize beach time. Now I regret it! Marianna's apartment is perfectly located: 7-8 minute walk door to Copacabana beach, 3 minutes directly to Lagoa, a little longer, maybe 15 minutes into the heart of Ipanema. Plus, with the options to use the bikes that are furnished with the apartment any farther travel is cut significantly. We really appreciated our morning bike rides around Lagoa. Cantagalo station is 5 minutes walking to facilitate easy, farther travel, as well.
We found the apartment to be perfectly furnished for our longer-term stay of 3 weeks. The internet works really well and we never had issues which gave us peace of mind as this was a working vacation for us. My wife and I switched between working in the living room and at the really comfortable nook created in the bedroom with a desk that both have amazing views out to Copacabana and Pao de Açucar. The view from the apartment, by itself, is worth the stay.
The kitchen is great with nice appliances with everything necessary to cook and a huge fridge to store food. Not that we cooked that much with so many really good restaurants nearby, many in walking distance. The bed is comfy and a nice touch to be able to watch TV from bed and in the living room. Having lived away from the U.S. for a number of years, I was impressed with the quality of cable channels now in Rio. I watched more live American sports in 3 weeks than I have in the past 5 years. Not that most will spend as much time in the apartment with so much to do nearby. Granted, if you're coming for a longer working vacation, I can't emphasize enough how comfortable the apartment is. We were very sad to leave!
Marianna and Francine were super responsive through our whole stay checking in on us periodically and helping quickly with small issues that will inevitably pop up during longer stays. The building staff are nice, as well, and the building is quiet (a luxury in Rio!). In all, we won't hesitate to try and stay in Marianna's apartment our next time back.