Help Somebody Please Help Me

I`m planning my quinceanera on my own but my dad says my step mom is suppose to help with it the only problem is that she didnt have her quinceanera when she turned 15 so she doesent want me to have one she`s only 20 and very jealous i dont want her to be involved with my plannings because every time i tell her any of my plans she gets all mad and says no which she has no right to say no to since i`m paying for everything my padrinos dont pay for she`s trying to ruin my special day and i need some good advise for example i told her i want to have damas and she said it was stupid and i shouldent even have chambelans i know i want chambelans and damas and i allready have them picked out and i told her i want to rent a hall because there are going to be about 300 people comeing and she said i should just have it at our house which is way to small and there wouldent be any danceing if it was at my house so as u can see i`m in a mess right now please somebody tell me what i should do she has such an influince on my dad i know she could end up makeing my special day a disaster and i have a feeling she`s going to do anything and everything to do it help!!!!!!