I can see both sides of it. On the one hand, the logical thing to do is let her go, don't risk trouble, because you never know how it might escalate, and where it might end up. But, on the other hand, as you say, in the heat of the moment, it is really not the money. It is the shock to your system when someone has the nerve to treat you that way. Every bone in your body says, "I'm not going to allow it." Then it becomes your will against their will. It's like a game of "chicken," seeing who will break first, and how far you will go to win the test of wills.
Once the battle of wills commences, then money has very little to do with it
To me, that would be the main thing right there, and I may have sat in police station a few hours more just to ruin her night, and make the point that she is not going to get away with robbery quite so easily.
In that regard, I thank you for your efforts on behalf of all us farang guys, who might just BF this girl some day without knowing any better. She won't be quite so quick next time to rip some guy off, now that she sees she might only end up with 500 Baht for the night, when she more easily could have earned the 1700 Baht.
This is hard to fathom. After all the shit you went through over the principle of the matter, it simply amazes me that you did not go back to the bar and get the BF back.
The only 2 times I have ever demanded a refund of a BF were both when the girl pulled a runner on me. That girl not only pulled a runner on you, but ran off with your money, as well, thereby adding insult to injury, and then, on top of it all, poured gas on the fire by having the absolute nerve to summon the MIB, claiming that you ripped her off. If that is not worth a full refund, then I don't know what is!