If you had the mod installed when you finished the great adventure, it would happen automatically. Otherwise, you'd use her illusion magic to change forms. To see if you installed it correctly, check the window's title bar to see if it says 'FFFox Mod Installed' or the top right of the title screen to see if my logo and the mod's version is there. If not, the mod hasn't been installed correctly, and you might want to go over each step of the installation instructions again carefully to see if you missed one, such as removing the old .wolf files afterward.