StreetFerret gets its city data from OpenStreetMap. If a street is missing or otherwise broken on the map, make sure that the street is in OpenStreetMap and is marked as a runnable street. StreetFerret will ignore streets that are marked private or not accessible to pedestrians.
If the street is correct in OpenStreetMap, the map may need to be reloaded.
You can reload the map by navigating to the city page and clicking actions > reload map.