The customer is NOT always right... and in this case the owner's explanation (you pay for the service, not the ingredients) of why it costs that amount is perfectly justified. My immediate thought before I even read it was "She wouldn't have had a problem paying £2 for tea, and tea is as cheap as if not cheaper than a lemon".
On the other hand, it does sound like the waiter was rude and dismissive at the time -- IF -- her account of what happened is accurate. Which it may not be - in my experience these "incidents" seem to somehow become worse and worse each time they're recounted by the customer...
Also, best practice for the owner would have been not to "rise" to the bad review. Keep it simple and professional. The irked customer is TRYING to annoy you... if you reply with a longwinded response like this (which is obviously passive-aggressive) you're just playing right into what they want from you. A clean, short, simple, cut'n'paste apology is essentially a way of saying "Yeah OK whatever

" and getting away with it