Most courts have ruled that for a pre-nup to be valid, both parties have to have sufficient time to review it and obtain legal advice in needed. Two days before the wedding would not be sufficient. Besides she is being put under duress to sign it.
Is she a child? Or a consenting adult?
Is she incompetent? Or in her right mind?
Did she sign because somebody held a gun to her head or because she perceived that she was acting in her own self-interest?
Was she defrauded or was she offered a contract whose terms were crystal clear?
People waive all sorts of options in business contracts and the courts generally uphold these terms -- except in pre-nups.