[@Spriggs27]
Or....she could just manipulate the earth and make one herself. Far cheaper and to her a lot less effort than having to not only convince the orcs to build it cheap but also having to gather the materials and lead the buildsite. Let alone gaining permission for the wall.
Also a lot quicker if she did it herself that way. (She is certainly a 'the only way to do it right is if I do it myself' kind of gal)