It shouldn’t need a vest. If she had documentation for it you have to allow it.

Service Dogs do not need to wear vests and they do not need documentation. If a dog is "registered" or has "papers" it is more likely that it is a scam because true handlers know these things are not required. As an employee of a business you are allowed to ask two questions: Is the dog required because of a medical need and what tasks is it trained to do. You have every right to ask the person with the dog to leave if the dog is not under the control of its handler or if the dog is being aggressive or making a mess.

this is why the phrase "the customer is always right" is stupid, it gives them more power than they ever deserve to have and the employee has to put up with it and sometimes get punished for it

My son has busted 6 fake service dogs at restaurants because of food he's knocked/thrown on the floor and the "service dog" has bee-lined straight to it because the handler has zero control over them; and also because the handler has let him pat their "service dog". I've also seen people try and pass off their therapy dog as a service dog; similar yes but they don't have the same rights are an actual service dog.

Being the U.K, and under U.K. law if you were fired for that then you have a very good tribunal case unless you were on multiple warnings. The court case would have gone nowhere if she had no identification that the dog was a guide dog as any decent solicitor (not lawyer as that is a U.S. word) would tell her.

since I worked security and dealt with this all the time there are literally only 2 questions you can ask 1: is that a service animal? and 2: what service is it trained to perform. emotional support animals are not included with the ADA's laws, and only dogs and miniature horses can be service animals. I have turned away several people with fake service animals. for those who pretend your pets are service animals are pets that aren't, that is illegal and can result in both a fine and potentially jail time