Four of us stayed at Raffaella's place during the Venice Biennale. The location couldn't be better - the apartment is half way between Giardini and Piazza San Marco.
The flat itself is great for two couples - it has two full bedrooms and both are equipped with proper beds - no bunk beds, sofa beds etc.
Raffaella and her daughter are helpful and welcoming, and the apartment is very clean.
I would definitely recommend staying at Raffaella's place.