Indeed, her second "s" comes out with a "z" sound when uttered by Siri's digital chords.
The likely scenario is that Streisand's retelling is inaccurate, perhaps Cook told her by the end of the month or maybe it's not the literal next update, as in iOS 10.0, but a forthcoming update coming soon.
Tim Cook, a gentleman that he is, agreed this should be fixed.
Streisand talked about the experience in an interview, where she offered some details about her tour in North America to promote her new album of duets called Encore: Movie Partners Sing Broadway. Anne Hathaway, Jamie Foxx, Daisey Ridley, Chris Pine, Melissa McCarthy, Alec Baldwin, and Antonio Banderas are among her collaborates in addition to a host of other film stars. It could be that the rumored September 30 release date would just be an iOS 10 update with the latter being expected to be released alongside iPhone 7. It also seems plausible, considering that Apple last week launched the seventh beta version of the OS for testers. This is, of course, a far more direct tactic than what the average user does, which is to take to social media or Apple's support forum and explain the problem/ask for solutions.
The tech giant Apple that runs a greatly developed operating system iOS is all set to release iOS 10 update on September 30. Thanks for the info Barbra, if only we could consider you a legitimate source of leaked information.
Streisand is excitedly expecting the change, as having her named recognized and pronounced correctly is understandably very important to her.