I also think that law enforcement's decision to pick up and take Paulus away was the reason that Natalee's mother didn't show up at the VDS house with Greta for the second meeting.
I bet the police didn't know exactly at what time they would apprehend the father, so they quietly told the mother to stay away. The mother does not appear to be the type to not appear for a promised appointment.
Someone gave her the word.
Leni
Note: House boarded up. Island homes may have hinged shutters on them in case of storms so they can quickly be closed and shuttered.