Sister in law controlling my life?

please help! i am married 6 years to my partner and we have a 11 month old baby! my sister in law(angela*) is taken over everything with our baby and has from the very start! my baby is 1 end of this month and she wants to organise the whole birthday party!(even though iv said we dont want a big do) she says we should have this, we should have that! iv told her no and that we only want a small do as it is too overwhelming for a baby having too many people around! she wants to invite all her friends! iv said no to her many times and she just never listens! she took over the christening on us too! im dreading my babys 1st birthday as she will be there and will want to bring out the cake and all the things a mother should be doing! i can see us havin a mive argument at it! how do i tell her politely to f*** off! im a very easy going person and i dont like being rude to people but its really getting me down! when she comes to my house she bosses my baby around and takes toys off him if he is being too noisy for her liking! i just wish i had the guts to stand up to her once and for all! im just so sick of her bossing!she took over our wedding day, our 1s babys christening and now this too, she has no friends of her own and spends alot of time in my house. i have started making excuses now so she wont call out! please help me, give me advice so i can stand up to her and have the party me and my husband want, not hers!!!!