I think the best quality for a woman to have is "patience". During life there are many things that happen that will require one to allow for time to resolve.
Patience is the state of endurance under difficult circumstances, which can mean persevering in the face of delay or provocation without acting on annoyance or anger in a negative way. it is best to exhibit forbearance when under strain, especially when faced with long-term difficulties.
It is also used to refer to the character trait of being steadfast in which one can wait for things.
It's hard to zero in on one quality when others demand so much of us. From experience I feel, multitasking, patience & lovingness. To do the above we need to be intelligent, trustworthy & openminded. Rather than beauty an attractive quality sure helps. Finally, our confidence in ourselves & those we love makes us come full circle.
i agree with sue she ( interesting name by the way . patience and lovingness are very rare qualities, especially nowadays. multitasking has always been many a woman's forte ( and what most men cannot do even if their life depended on it ).