Very nice apartment in a location that's not too far from the city centre (about 20 mins. from the Plaza Moyua) and only about 5 minutes on foot from the old section of town (which is the more lively district). We travelled regularly with the metro: one of the stations is located around the corner. Only one change was needed and three stops in total to get to the stop for the airport bus.
There's a supermarket around the other corner for anyone wishing to use the facilities to self-cater.
The bathroom is fairly tight, but should not really be an issue for a couple of guests.
We didn't meet Carolina in person, but Lali, who showed us around, was very friendly.
Bilbao is full of delights with fine architecture, cozy pintxos bars and at least two fabulous art museums. Highly recommended.