"She is paying only for the wine."
Translation:היא משלמת רק על היין.
As near as I can tell the multiple choice options seem to be generated from all acceptable translations of a sentence. When translating a sentence freehand, it allows you to use words that haven't been learned in the lessons in case someone with prior knowledge tries to use them, so those answers are marked acceptable and get thrown in the pool for multiple choice.
As I already wrote to dangoodpuns, "pay for" in Hebrew is לשלם על. That is simply how this preposition works. On the other hand לשלם בשביל would mean "pay on behalf of". It would work if you paid something on behalf of your brother, for example לשלם בשביל אחי, but it doesn't work with wine.