there is a law out there that makes it so the people with disabilities cannot be denied if they have a service animal... albeit a store, or airline or even apartments whatever... they cannot deny a person that has a service animal if they have the right documents for having the service animal...
for me I had my therapist type up a letter... and she stated that I needed my Gracie for emotional support reasons... and that she was a key role in my recovery. there is no where that says that the service animal has to be a dog or a weight restriction... I would think that your friends golden retriever would be ok albeit she has the right documentation... if you have any other questions that I might be able to help you with dont hesitate to ask!