Could it be possible that Beth's attorney advised her not to go? Or Aruba authorities?
I can certainly imagine that the authorities might tell Beth that she risks complicating the investigation if she keeps on pressing the van der Sloots for information. Not saying it happened, but it would surprise me if she were not advised to cool it with them, for now.
That crossed my mind too - it seemed sort of out of character for her to be so agressive with them yesterday - then not go today when she insisted. I figured someone probably told her not to do it.