Sandra's place is very convenient - it's one block from the tram that comes from Rotterdam Central Station and is in a neighbourhood with food + groceries + banks.
We were able to rent bikes from Sandra at a very reasonable rate and explored Rotterdam on bike.
A great host who was actually improving her home with some new furniture and dishes during our stay. The room is not large but it has everything that you need. There is a workshop next door which has a fridge / coffee machine which you can use as well. There were no workshops going on during our stay which meant we had that side mostly to ourselves.
Just a heads up if you are travelling with a friend. The shower in the room is "open" and privacy may be a bit of a challenge in that regard.