Hen night problems

I have arranged my sisters hen night and have tried to include all her friends. However, her best friend has been extremely difficult during the entire planning, I have had to move dates to suit her, and work around her for all the planning. I have finally done everything and it has cost me a huge amount of money, now my sisters best friend has gone out and arranged things I have already sorted out without telling me (yes, I did let her know beforehand!). Now I am getting v angry that there will be a row on the evening when her best friend decides that she wants all her gifts and ideas to replace mine (as there is duplication we can't have both). Am I being petty in refusing to replace everything? I have paid out for everything so far, and have worked my bum off to get this night off the ground, and I don't want to cause a row but at the same time it has really got to me that her friend can be this selfish in doing nothing and then stepping in at the last minute to make it look like she's done all the hard work. Please help ladies!