Flying for the South African AF as a female is by all accounts is unlikely if not impossible.  If you want to fly for the USAF or USN, the first thing you have to do is get US citizenship.  Also be SURE to have UNcorrected 20/20 vision.  If you're visual acuity is below that, forget it.  Flying for the Navy will also require you to  have no color blindness.

The next thing you must do is become a commissioned officer.  The surest track for that is to get into a service academy (US Air Force Academy (USAFA), US Naval Academy (USNA), or US Military Academy (USMA)).  The Army has no fighters, so concentrate on getting into USAFA and USNA.   Although you can cross commission from USMA into either the Air Force or Navy, don't count on it.  Major in a technical/engineering area and keep your grades up.  This will help ensure you will get your first choice as to post graduate specialty area.

Once in the undergraduate pilot pipeline, get good grades.  The fighter slots are competitive and good grades will ensure you get your first choice.