Thank you for posting the picture of the label. Doing so gives me clues as where to begin my search (as in just "Miss Sandy" or for "Miss Sandy of California"). I searched many of the databases I use and found quite a few ca. 1972-1982 ads for Miss Sandy (and Miss Sandy of California) items. I have not yet been able to find any information about the firm, though, but I will keep looking. The difficulty here, as I am sure you found, is that searching for "Miss Sandy" brings up something like 48,000 hits on Google. I tried narrowing the results with searches such as:
-- "Miss Sandy" California
-- "Miss Sandy" apparel
-- "Miss Sandy" fashion
-- "Miss Sandy" designer
-- "Miss Sandy" dresses
-- "Miss Sandy" clothing
and the same searches using "Miss Sandy of California."
I searched databases specific to CA newspapers, but was unable to find anything other than ads. I also tried searching the trademark and patent gazettes, but only found a reference to a 2006 trademark for "Miss Sandy." I will try again later, but I regret that I am less optimistic that I can help, as I originally hoped.