the Queen's street cred

if you have street cred, it means you don't have street cred.

I think that "street cred" was used ironically in this instance, because the point of the article was that any appeal provided by the old GJ was based more on a sense of spectacle than anything else. No one cared, no one was particularly entertained, and using a nonsense term to refer to the Queen's connection to the people only reveals how out of touch she truly is.