I think you should/could do both. i mean, even though your almost 13 the whole birthday cake and singing thing isnt 'stupid' ,or 'out of date' . People may say that but in all reality it never gets old. As for the thing about wanting to have a 'big' party or not i cant really give you any words of widom there. You and your sis are going to have to come to an agreement or just have separate partys all together.