Before I even found this thread I wondered would the Strathmore Tiara be used by Catherine because technically she will be the next Queen Consort after HM QEQM and it would be an homage to her. While there is talk that Camilla may become a QC, for now, they still refer to her future title as Princess Consort.
Technically Camilla is the next Queen Consort as the wife of the king is the queen by law and the next king is her husband Charles. To deprive Camilla of her rightful title as consort of the king it would need legislation which is not even discussed at the moment. It doesnt matter what is said about Camilla's style once her husband acceeds to the throne by law (and thus: technically) she is the next Queen Consort if both she and her husband live to see the day HM dies.
As for the Strathmore Tiara: it was purchased at a time when the nobility still gave jewels to the Royal Family (Think of the "Girls of Great Britain and Ireland"-tiara - the "girls" being the peeresses who gave the tiara as a present), so it seemed a suitable gift of the Earl and Countess of Strathmore to their daughter who was to become a Royal, even if only a minor one as the daughter-in-law and future sister-in-law of the current and next king. It was never meant to be a tiara for the Queen Consort or The Princess of Wales. In the 1920s thoughts about the suitability of tiaras for a Royal lady of a certain position were common and surely are still thought in the Royal household (think of Sophie Wessex' tiara!), thus I don't think they'll find the Strathmore-tiara suitable for Catherine as a future queen.