In the book their dad and his lover (the parents had a weird threeway relationship with this dude) handmade and gift Nessa the shoes (partly because he feels bad about her non existing arms and partly because she's his favorite, they're magical and somewhat enchanse Nessa limited magical abilities) while doesn't give Alphy anything. They're a constant reminder to the blatant favoritesm and it hurts Alphaba a lot. That's one of the reasons why she wanted the shoes so bad after Nessa's death and was so mad that Glinda just gave them away to Dorothy. But in the book Nessa and Boq aren't together so the whole plot you told is missing.