@rosaleen,
That phrase is Greek in origin, not Latin. No-one really knows who said it first, some say Pythagoras, some Heraclitus, some Socrates.
In our alphabet it is spelt "Gnothi se Auton" (pronounced "nyoh-tee seh owton"). The exact translation is "Know thyself".
If I were her though, I would get it written in Greek as it's far nicer and unique, and with a bit of mystery thrown in.
γνώθι σαυτόν
Hope this helps.