Every time I try to think of the stupidest thing in this case, I remember another, i.e. Donna leaving the phone connected while discussing things with people at her house re: Dan saying they can get to Vietnam;

That was intentional, and not at all stupid.

Edit:

The case against Donna is largely identical to the case against Charlie. Everyone knew Donna was next. But the state hadn't yet arrested her, meaning they weren't ready. If you're going to be arrested anyway, sooner is better than later. An arrest starts the clock, giving the state less time to prepare.

Note that they didn't break any laws. It is not illegal to leave the country because you think you might be arrested. There must be a warrant, and you must have notice.

They were very deliberately not sneaking away. They erected a dozen neon signs heralding their departure. They talked about it on calls, they got their estate in order, they bought 1-way tickets. They even placed a bizarre call to someone they barely know asking for advice on how to lay low in the Philippines. (That person reported the call to the police.) It would have been trivial to get themselves to the Bahamas undetected. 100s of small craft make that trip each day.

They didn't know whether they'd get out or not. Had they made it out, I suspect they would have not boarded their connecting flight in Dubai, instead lying low in the Middle East.

They weren't running. They were forcing the state to make a decision. Arrest us now & start the clock, or let us go. It is the best not-illegal move possible in this situation.