The only unidentified credited actor is
Ángela Tamayo, pictured here in a couple of 50's film roles and some images found online. IMDb say she should play the second companion of Cesar, however their identification of the role played by Teresa del Rio as first companion of Cesar is incorrect, so I doubt this one would be either.
1. This is the girl who appears with Teresa del Rio at the party, however her role is smaller, so less likely to be credited. I think her face is too thin to be Tamayo.
2. This is a speaking role of film star Elisa Torres, which would be more likely to be credited, but she doesn't really seem like her to me
3. Then there are the 2 losers of the contest. This one again seems too thin faced to me.
4. Of the 5 this one seems the most like her in my opinion. She seems a bit young, but could just be made up to look younger?
5. The only role that could actually fit the role description on IMDb would be this one, but to me she seems the least like her of the 5.