Well, that's the most logical argument I've heard since this began.

She aims to kill Shepard. I'm sure the concept of revenge isn't a foreign art to you, Mr. Harkness. Considering I stand to benefit from Shepard's death as well, I felt it was in my best interests to agree when she sought out my help. Whatever's going through Martha's head at this point isn't my business and I don't intend to pry into it.

That being said, I'm sure Martha's the sort of woman who will run this through every available channel if you try to shut her down, so if that's your intent, I doubt it will make the situation any better.