The owner also thanked customers for all their support over the firm's 144-year history.
Lisa Keogh says the situation at the Angus secondary is "so wrong on so many levels" but was told pupils voted in favour of shared toilets and changing areas.
A photo of two campervans parked outside the property was circulated to officers.
Pictures show officers closing one lane of the road while dealing with the incident.
A festive market had been due to run in the city centre - but failed to appear last week.
It comes after an 18-year-old was taken to hospital with serious injuries.