It means it that she makes no sense to any one but another woman who also makes no sense.
Women use that phrase when they don't understand their selves well enough to explain their selves to you in a sense where you would see EXACTLY what they are saying or feeling. Do you understand me? LOL
It means she is a woman and you are a man...
It means you should tell her to help you to understand. ( if you care about her) :)
if I could heart it twice I would! lol