Like so many others in FD's world, MT was in way over her head with him. He is a domineering, malignant narcissist, very skilled at manipulation. It's another story with MT. You and
@afitzy have thoughtfully analyzed MT's character and the dynamics of her relationship with FD. FD presented himself as a extremely wealthy, handsome (at least to some), charismatic and charming father who was, on the surface at least, a devoted father. IMO the two met at some type of sporting event, possibly with their children, clearly out of town. Who knows what BS he fed her about his life in CT? You can bet he didn't tell her whose money he was so freely spending, and instead presented himself as a sophisticated, well-educated and wealthy businessman, the contractor of exclusive luxury homes, the total package. FD went to great lengths to maintain that veneer.
I imagine he was exactly what MT was seeking; the fact that he was married did not seem to bother her at all. MT strikes me as a very weak person, easily manipulated and someone looking for the Good Life. She and the father of her child never married. Unless one of them was fundamentally opposed to marriage, that tells me it was never a particularly durable relationship. I would be very curious about when that relationship ceased. Did it stop when FD and MT met? Did she also cheat on her boyfriend with FD, as FD had with his wife? This is not a question of 'morals', it is a question of character, of honesty and integrity.
I also agree that her move to CT, indeed her willingness to move into the former family home, is very telling of her character . Of course, you can be sure that FD was continuing to feed her a series of lies. We have heard those very lies coming from his lawyer's mouth. Jennifer was a terrible mother, crazy, possibly a drug addict, she was trying to steal all his money, destroy his relationship with his children, destroy his business, his life. I am sure the list goes on and on. Did MT always believe him or did she come to realize what she had gotten herself into? In my mind, she sure seemed to be enjoying the Good Life, paid for courtesy of the Farber family.
At some point though, you can be sure she saw who he really was. By that time, she is working for him, living with him and completely entangled with his life. She wanted to please him. She wanted to do what he told he to do and that is precisely what she did. Like others before, pleasing him probably became an exhausting full-time job. FD has the type of personality that "wins" by domination.
One of the reasons I believe she had, at minimum, pre-knowledge of Jennifer's murder, though, is the way she acted in the days after Jennifer's murder and seemingly continues to act. Whatever her prior entanglement with FD was, she is now free of him. Despite this fact, until at least her last debriefing, she was continuing to lie to protect him (and herself)! Given the opportunity to tell the truth it appears, at least for now, she has elected not to do so. Whatever she "did or not do" because she was living with FD, and dependent upon him, she is not in those circumstances, now.
Where is MT's anger, her outrage that this man has dragged her, not to mention her daughter, into the middle of a murder? I know, I know she had already chosen her own wants over the needs of her daughter, but still. The decisions she appears to be continuing to make are not that of a normal person. IMO she is under the influence of some drug even now, either xanax or some kind of SSRI. Her affect is too flat. Compare the recent way she acts in court/on TV with the hot mess she was when she was arrested. From the latest AW, we know she has been inconsistent and vague in her answers to LE, and that makes no sense. Is she trying to avoid facing her own moral culpability? Is medication interfering with her ability to think clearly? Does she still foolishly believe FD "luvs" her? Mr. Bowman has the difficult job of providing MT the proverbial guiding hand of counsel so that she understands precisely what is at stake for her. I don't think she gets it yet.