I don't think she would had even tried to use fear manipulation on a human. The one time she had to deal with humans that weren't Rokurou or a cute girl is when Debby was up against thugs, which... Well, they freaked her out at first, but... Well, Chapter 48 (the chapter the thugs showed up) shows that if anyone tries to mess with Rokurou, Debby will not hesitate to **** you up. Heck, she blew up a small part of a forest even though the thugs were merely freaked out by it (side note, what the **** is up with the author and trying to show off Debby's strength with 1-psi-overpressure explosions? Come on!)
Chapter 67 only further shows the whole "mess with Rokurou and Debby will **** you up" deal. Honestly, the relationship between Debby and Rokurou gets stronger throughout the series. In Chapter 1, Debby would not've hesitated to kill Rokurou had it not been for Rokurou's quick thinking. In Chapter 71, when Debby thought she FROZE Rokurou to death, Debby freaked out and was later crying while hugging Rokurou's arm. It's unrelated to the debate, sure, but I felt that was an important part of Debby's character development that I wanted to bring up.