Her or her lawyers would present her case with as much evidence as available. For example: Police reports, hospital rape kits, injuries, witnesses, etc. - anything proving that such a crime was committed. If she has four witnesses it is better, but if she is unable to produce four witnesses her case can still be proven.
The four witnesses or a confession would prove that the man committed fornication. He would be stoned to death if he was married and receive 100 lashes and exile if he was not married. That is the punishment for fornication. If she is able to prove her case in the absence of four witnesses and a confession, then the crime is showing transgression towards the Muslims and the judge can choose between four punishments: death, crucifixion, cutting off their hands and feet from opposite sides, or exile.