My boyfriend and I had a lovely time at Mariana's. It is just as described - small but cozy, with some basic amenities and a futon bed. We made two delicious dinners (the grill was perfect for fresh fish from the Dolphin and veggies from the farmer's market), and they kindly lent us a big bowl to make a salad.
Her and her husband were incredibly accommodating when we asked if we could leave stuff in their garage when we went backpacking for a few days.
Princeville is a great location if you're looking to see north shore sights, but we were surprised to find that it's more like a gated community/planned suburb than the neighborhoods we're used to. That said, Mariana's house is beautiful and the entire area is immaculately landscaped. We had a very pleasant few days and would absolutely recommend a stay at the studio!