There is a simple explanation for that: she wanted to inflict pain and hear his screams. Listen to the way she spoke to him as she was doing it. It felt like one was watching a scene from Criminal Minds.Not to mention stupid. Why she couldn't scan him to see where the technology was!!!
Unless the borg elements are somewhat "cloaked" in the body that kind of "exploratory surgery" is just imbecilic!!!
Do you realize that exploratory surgery is practically obsolete NOW!!!