I don't think she manipulated Don into anything. As you stated he seemed like a shitty person, based on what was said about him in the documentary. I think a couple of people even admitted that he was a womanizer. He likely was a serial cheater who was always involved with more than one woman. For the record, I too, do not buy her story of him seeing her walking down the street and suddenly deciding to stop and ask her to ride with him because he needed to "talk to someone". When I heard that story, my first thought was, married or not, Carol was prostituting and that's how she met Don. Or they met at a club where she was stripping.
She claimed she left home at 15 after being raped by three men, because her family were Christian and thought the rapes were her fault. I understand the supposed attacks happened years earlier, but she didn't seem traumatized by it at all, and mentioned it very casually.
My question was, where did she go and do before meeting and marrying her first husband? I believe it was stated that she didn't marry him until she was 18-19. Also, how did she reconcile with her family? Or was that whole story about her being raped and leaving home a lie? There's no way to know for sure because of the inconsistencies in her stories.
Carol's reaction to her husband's death/disappearance was just odd. She couldn't have cared less that he'd disappeared. Even when he was finally declared dead, five years later, she didn't bother to have a memorial service for him. Regarding his death/disappearance, I believe it is an Occam's Razor situation. If she was involved with his disappearance/death, she likely did kill him on the property and bury him. The property was what? 40 acres or something? When they did an overhead shot of the property there even looked to be a lake on it. It'd be much simpler to kill him and bury him there, than to come up with an elaborate plan to pay someone to fly the plane (a plane he could apparently fly himself), take him out over the ocean and push him out of said plane. If she killed him, she likely did it in a field somewhere on that property, then buried him out there. It would be harder to find evidence on so many acres without a very thorough search.
The speculation she mentioned about him being pushed out of plane over the ocean, could have been nothing more than a story to distract from what really happened.