Trying my best – no one outright assured denim however tznius is NOT all about clear cut halacha. There are a lot of gray areas, where the natural sensitivities of bnos yisroel should kick in. As i once heard – “tznius is a sensitive mitzva given to sensitive women” meaning tznius requires A LOT of sensitivities and is not so clear cut- women who are naturally blessed with these inner sensitivities should use them! (halevai we saw these natural sensitivities being practiced by all.
And see Rav Falk regarding denim “chukas Hagoyim”… not exactly what a queen would wear. Aren’t bnos yisroel – Bnos Melachim?