yay!!! Tell your friend congrats from one of her sisters to be. 
As far as posting - do what makes you feel comfortable.  If you want to be mysterious - go ahead 

 and everyone will respect that decision.*  You don't have to worry about rush rules - the only time that would be a prob is if a GCer from your school would email or PM you within the "silence" time.
*
or I will get medieval on them.