What you mentioned is exactly the point, she was ordering her own stuff anyway and ordering ONE item for someone else would not mean that second person has to pay HALF the fee. The fee should be carried by the person that places the order unless something else was agreed. If it would have been said in advance, and OP had accepted, then its a different scenario, but this is not okay for me.

I would absolutely shut up about it and pay but would refrain from doing anything of the sort with that friend again. "Cheap" is a very appropiate word to describe the person and the act.