Well, yes, justice is supposed to be blind. It would be nice to extend that to immigration.
Also, jet lagged people who are afraid of authority tend not to present the best case for themselves under pressure.
A whole bunch of lessons learned.
And all that can be applied to entry into the USA as well. In fact all countries of the world!
Being jet lagged is not an excuse. I can't see the CBP being sympathetic if it was a UK national presenting at the US border with the same story.
Your friend wasn't refused entry just because she said she was going to volunteer at the beer festival but because other elements of her story were suspicious and the answers given by the people the immigration officer contacted probably did not tally with hers.