Thanks Fool for the pic.
Are you positive that is Mireille??
I can clearly see the likeliness but 19-year-old Mireille didn't get her breakthrough untill November 21, 1965 in a French TV-program where she won a singing contest. Her debut album "Mon Credo" was released in 1966 and sold an astonishing 1,3 million in 5 months.
Elvis filmed Spinout during February thru April 8, 1966 so Mireille would have had to go to the US at the same time her debut album was released and she was just starting to build a career in France.
I've never heard of a meeting between Elvis and Mireille but it sure looks like her.
By the way, for those who don't know Mireille Mathieu, she has a fantastic voice that gives me goosebumps just like Elvis does at times.
Here's a pic og Mireille from around the same time as Elvis filmed Spinout