The manor before she took it over was last occupied a century ago before the strange sighting started, causing the owners to abandon the idea of living in such luxury.
In order to pull other people to buy the place, despite the many risks and dangers people wanted to avoid, the castle was renovated several times, leading to its current state, which was then further changed when Diamond took over.
That process was done through Andrea, a decision that she would never regret. Andrea's projects were always successful and she would never take that achievement away from him.
As the people who last lived at the manor weren't the original people who started living there, and neither did the architect and owner of the manor in the first place, many secrets were hidden and it seemed like not many people managed to find them in the first place.