Pamela Tiffin (Slight spoilers)

I finally sat thru this film. Well photographed and stylish, but oh what a journey to the revelation of the killer. Anyway, what was the point of Pamela Tiffin's character?
Spoilers:




She wasn't the killer or a victim, or involved with the killer.
She appears for about half of the film, and decides to get married to someone else, and then bye.
Was she hired for marquee value for American audiences?