In a later conversation between Frank and Dolly, what do they discuss concerning her mother?

In a conversation after returning from the station master's home, Frank tells Dolly that the house was lonely while the children were gone. She responds they were not away very long. Dolly then asks her father if he knew what her mother was doing. Frank replies he did not. Dolly responds that she anticipated as much and adds that her mother sent them back since they were not a comfort to her. Dolly also relates that she believes her father required too much of her mother. Frank disagrees and tells his daughter he knows his own mind. Furthermore, her mother does as well.