Tree trunks don't grow taller. The height at the point where the limbs grew will be the height forever so if a new limb sprouted at the 5 ft level, it will always be at the 5 ft level. If your friend chooses to keep the walnut, choose three evenly spaced and appropriately angled branches to become the new scaffolding branches for the tree. The chosen branches should be growing up, not sideways or down.
In commercial walnut orchards, the trees always branch just a couple feet above the ground but I have never hit my head on a walnut tree. A tree with a 4 or 5 foot trunk should be fine. The branches will grow tall and continue to branch higher. If your friend wants a tree she can walk under, this tree will be walk-underable.
Another advantage of keeping this tree is that the roots are established so new growth will be faster as the canopy catches up with the roots.