Kairos means Time.
It is of Masculine gender.
There is a feminine version of teh name, Kairo (pronounced keh-ROH, and written with an omega). It is a beatiful name, it is recorded in *The Lexicon of Greek Personal Names* (
http://www.lgpn.ox.ac.uk/). I am afraid I have never seen it used in contemporary Greece.
So I would never recommend KAIROS for your girl -- it is a guy name! -- but Kairo might be an interesting name! Just make sure you also give her a more conventional middle name (not , say, Moon Unit) so that she may choose when she grows up!