It depends on what she means by 'middle period'. Usually, the middle period is considered Human, All Too Human, Daybreak, and maybe the first four books of The Gay Science. The works after that are considered his later period, sometimes scholars also take the works of his last sane year (1888) as a separate period, but that is debatable.
The middle period called his 'Enlightenment'-period. In contrast to his previous 'romantic' works (Birth of Tragedy, Untimely meditations), he has a more favorable attitude towards reason, science, and the Enlightenment. His attitude is less historical, more reflective.
In his later periods however, he turns reason against it self, tracing the lofty ideals back to the not so enlightened beginnings. Paul van Tongeren provides a good introduction on Nietzsche's periods in Chapter One of his Reinterpreting Modern Culture. An introduction to Friedrich Nietzsche's Philosophy.
For example, Daybreak 133 is about pity
"What in the end distinguishes men without pity from those with it?
Above all to offer only a rough outline here too they lack the
susceptible imagination for fear, the subtle capacity to scent danger;
nor is their vanity so quickly offended if something happens that they
could have prevented"
Contrast this with
"Nothing is more unhealthy, amid all our unhealthy modernism, than
Christian pity" (The Antichrist 7)
The commonplace view of Nietzsche is, in this case, based on his later works, so it is kind of a moot point Abbey makes, if this is all she says.