I have never seen any verifiable evidence that Queen Alexandra wore (or owned) fakes.
I am familiar with the story of the fake pearls. That was in the newspapers at one time, but I have always felt it was more of an amusing tale than something based on facts.
As far as I know the only pearls which Queen Alexandra wore which we know little about is the long multi strand necklace (strung in the Indian taste). To be honest, I cannot see anything in these pearls which would substantiate the theory that HM wore fakes. The pearls in the necklace are small and, as none of the photos give any idea of the quality of the pearls, it is impossible to gauge whether they are real or not.