In looking at the total picture, here we see Grant. He's shown himself to be quite inept at doing even basic things like buying a saw or blades. He's consulting everyone left and right. And then showing how indecisive and a little loco, but not aggressive in the police interrogation room. And even Amanda herself (and Sha) testified that Grant would start something and never finish it, that everything he tried was a dismal failure.
And then there's Amanda on the stand - very sure of herself, doesn't even show a lick of emotion, particularly sadness or even fear. To top it all off, we hear Ms. Patsy use that sarcastic tone when reading her "love letters" to Grant. If anyone knew the dynamics of their relationship, it was Grant's mother.
ETA: The question for me is who had the most to gain from Laura's death. In my mind, it was Amanda. No more child support. No more courts. No traveling. No having to deal with Laura. Grant could not care less. He's used to people taking care of him and schmoozing. He would have merely found another "host" for his parasitic azz and dumped their daughter with his mom and Amanda.
We have some pretty educated jurors and even one has her degree in psychology. So, it'll be interesting to see what they decide.
Once we get past viewing Amanda as the subservient, manipulated, terrified wife of Grant, a new picture definitely emerges. Grant seems to rely on his mom when he needs to put his family in storage. Laura went to Grant's mom when she needed a place to stay and an income. Grant contacted his mom about needing a place to stay and money for Amanda, Lilly and himself, but I suspect that once Amanda and Lilly were with his mom, with Amanda working in the daycare (just like Laura in the past), then he was going to leave. He would have found another female investor (like Amanda) and spent his days traveling, getting high, and partying.
I don't understand why Amanda thought that murdering Laura was a ticket to remaining in Grant's life, but it does appear that she perceived Laura as an obstacle in her dream of having a life of travel, fame and celebrity with Grant.
I think she was a desperate woman, afraid of getting old, and painfully aware of the fact that the time for play acting as a child woman was almost at an end. She put all her eggs in one basket with Grant, and like an investor that sees the stock value decreasing, she chased good money with bad until, in desperation, she believed that removing Laura from the equation would solve her financial and love related problems. I think that Amanda played a major role in Laura's murder.