The research she cites showed that in performing a task that involves both types of concentration, such as recognizing faces, better performance on the cognitive task was seen when daydreaming was also employed. However, "this conclusion is only applied to tasks that support each other."
I don't have any research to back up my extrapolation, but this may also apply to fiction writing. The novelist spends hours coming up with plot and characters for a story, a process similar to daydreaming. It can be proposed that such mental work might actually increase performance on externally focused tasks.