Praise be to Allaah.
There has to be a walee (guardian) and two witnesses to any marriage, because of the hadeeth, “There is no marriage except with a walee” and “Any woman who gets married without the knowledge of her walee, her marriage is invalid.” Therefore this marriage contract must be renewed, if her walee agrees to that, in the presence of two suitable witnesses. See Question #2127.
And Allaah knows best.
Sheikh Muhammed Salih Al-Munajjid