Idk if anyone ever pointed this out, but I dont think Kakashi is as innocent as people think he is. On chapter 69 pages 12-13, Oro said "You've already gotten your hands on it..." also the same scene in the anime he said something like "You got what you wanted" and Kakashi tensed up and got pissed. That shit seemed suspicious af to me. I think he knew about the sharingan and its power and wanted to increase the power of it. Long story short, I think he killed her on purpose. She had to have been a spy, and he chose to kill her knowing that he would awaken the MS.