Nice of you to jump in, but you’re missing the real reason she couldn’t buy that coffee. It has nothing to do with the EU or money laundering.
The issue is that small businesses can’t easily break large bills—it’s expensive for them to keep enough cash on hand for change. Big establishments can handle a €100 note without problems, small ones usually can’t. I spent even larger notes without any problems in larger establishments.
This isn’t something new this problem has existed in one form or another since the dawn of money.
We can see a similar situation in the Bitcoin Lightning Network. Try sending or receiving a large amount via the Lightning Network on a small, poorly connected node—it won’t work because nodes don’t have large amounts sitting in their channels. The solution? Connect to a larger node with fat channels. To draw a parallel with her situation, she could have gone to a larger establishment and would have been able to pay there with that bill.
It’s fine to push for Bitcoin I do it all the time but we need to stay realistic about the world around us. Over-exaggerating doesn’t help anyone in the long term.
That said, I fully agree: study Bitcoin!
Stay positive, keep pushing, but be realistic.