The logical inference based on the passage is:
a. The author feels that an important character has been left out of the film.
This can be inferred from the statement that in the documentary, there was a Z-Girl along with the Z-Boys, suggesting that the presence of a female character was significant. The author's implication is that in the current situation being discussed, the inclusion of only Nikki Reed as Kathy, Tony's sister, is lacking compared to the previous documentary.