Again not the same.
Everybody expects road safety. In fact we have a right to that assumption because everyone is tested to a certain agreed standard in order to pass a driving test. Same with catching a flight. I expect a pilot to be trained to whatever level his certification body agrees is right. And it's interesting because no one catches a flight thinking 'this plane cannot possibly ever crash' no. They catch it thinking , well it could crash, but the risk of that happening is very low statistically. Same thought process getting in a car.
You walking into a high risk environment that has the potential to render you dead in mere minutes and expecting me to be totally infallible whike also serving 5 different milks and a hundred customers is unrealistic. You are making a minimum wage worker more culpable than a highly skilled and paid airline pilot.
Human error will always happen. If milk can kill you the only way to be 100% certain is to avoid it.
Actually it is a privilege to be able to avoid your triggers. Some of us have airborne or unidentifiable, untestable allergies that are extremely difficult or impossible to avoid and live only by the grace of daily mega doses of antihistamine alongside monthly injections in hospital.
You don't have the right to put that responsibility for a trigger you can easily avoid by walking past a shop on some poor random person and make their entire life hell when it goes wrong, like this poor worker is experiencing. The guilt will live with her for the rest of her life and she's been dragged to court all because the mum couldn't just refuse a hot chocolate and probably feels guilty.
I myself would do the same as the mother, but I hope in years to come I would realise my expectations were not realistic. This is not even the same as the Pret scenario.