Agreed, but if all she needs to do is move a shit ton of stuff between two computers, and doesn't want to buy more than the external drive she already has, then why not?
If all she needs is some additional storage without additional purchase, just plug the drive into one of the computers and share it over the network from there. Agreed that the convenience of having the storage available over the network probably outweighs the speed issue. But I have just used the sneakernet method when copying my library of movies from one computer to another.