No, "c'est gentil" means that something is nice, not someone. For instance, something someone just said, like:
- tu es si jolie aujourd'hui ! (you're so lovely today!)
- merci, c'est gentil. (thanks, that's nice of you)
"c'est une femme" = she is a woman. The reason for "she is" to be translated to "c'est" is that it is followed by a modified noun = une (modifier) femme (noun).