Why did she retire?
Her last film role was 1976 when she was only 38. It's a shame she didn't continue appearing in movies through the late 70's and 80's at least.
You can see pictures of her from The Arena (1974)
https://www.imdb.com/title/tt0069729/mediaindex/?relatedNames=nm0626219&ref_=tt_mv_close
and she's just as beautiful as ever. While I know some people and many producers thought/think a woman's as an object of desire is done by their late 30's, I think Rosalba could have done these kinds of roles for quite some time.