Selfish or reasonable?

So my SOs best friend is doing a gender reveal they will be giving us the envelope with gender tomorrow and want us to order a baseball they can hit for it, unfortunately I can't find any to be ready by this weekend and if I do they are pricey about 40-50$ something we definitely would not spend on a gender reveal ball. The girlfriend is upset and stubborn saying we should have purchased a set of boy and girl earlier and does not want to do anything else like a ballon,cake or smoke ? At first I felt bad but now she is really expecting us to pay for the ball!! Like has no plans for any other reveal and will not change her mind am I wrong for not caring anymore and going to purchase something else instead? At first I felt terrible I thought it was cute to break the baseball but now after the way she's acting and demanding us to pay I could care less