So, the Schengen passport holder has a slightly different Visa on Arrival limit to her husband as a Brit only gets 30 days and can do border runs to renew. Schengen passport holders get 90 days multiple entry but on the 91st day they have to leave for the next 90 days and cannot do border runs. So its entirely possible (passport expiry aside) that she could have got this wrong and arrived during her embargo period.
So even if she had a valid passport, its actually still possible to arrive in the UAE and be unable to get entry, or to not be able to buy anything on arrival.
But as others have said, the reason was not drink as there were at least two or three options to eject her.
Her issue now, having been deported, is that she cannot come back and cannot transit through the UAE for the foreseeable future.