According to the She's Always a Woman Songfacts,the lady Joel was adressing in this song was Elizabeth Small, and they first got together when she was still married to Joel's drummer Jon Small. Billy Joel was so tormented by his affair that he tried to kill himself by drinking furniture polish. The pair later married.
She can kill with a smile, she can wound with her eyes,
She can ruin your faith with her casual lies,
And she only reveals what she wants you to see.
She hides like a child but she's always a woman to me.