The apartment is wonderful - cozy, well-equipped and with a good location. We haven't seen Maria, but her niece Sabrina met us and helped a lot, answering all our questions really quickly.
The apartment is 20 mins from the railway and bus stations, and 5 minutes from the square with multiple cafes and shops. On the other side of the railroad (15 min), there is a big supermarket Esselunga. Also in 10 min walking you can find the D'Ambrosio trattoria, which is worth visiting.
Summing up - big thanks to Maria and Sabrina, would definitely stay at this flat if returning to Bergamo!