Please all stop pretending BA is some innocent flower, manipulated by some cunning conman.
Read back through his posts. Intelligence is not DD's strong point. How those dead eyes could be interpreted as charming is beyond me.
On a human level who cannot feel sorry for her. The whole situation is horrific. Those poor kids.
But I have a hypothesis. BA is bright and driven, and she must have seen through Dirty Dan. We know she knew about all the doubts, because she was reading them here and responding. We know she made up lies in response to the questions we were asking.
I believe she is a sociopath. Sociopaths have a burning desire to win. It will override pretty much everything. I think she went with Dirty Dan to get back at Gramps. The tattoo, the holiday, the rushing, the moving. I think she was talking directly to Gramps. It sounds nuts that someone would throw their life into such chaos, to win some argument that is in her head, but sociopaths will do this. Win what? Show gramps he wasn't that important. That he was replaceable. That she could have a new version of him, a version who wanted to be with her kids, in double-quick time.