How to handle overbearing mother in law with my son?

my husband and i have a beautiful son that i gave birth to last year and he is about to turn 1 in march. ever since he was born my mother in law has in a polite yet rude ( if you know what i mean) way tryed to tell me how to handle raising him. tells me what to dress him in and how to brush his hair and what kind of games i should play with him. i would appreciate this if it were friendly advice from one mother to the next but she tells me that what she says to do is basically the ronly right way. i am a great mother who has been there for every moment of my childs life from day one and never asked her for anything and i just don't deserve it. i tryed to just brush it off but lately it has been worse. she has given him foods that i ask her not too and a couple of days ago she gave him a snickers bar and got peanuts stuck in the back of his throat that i had to dig out. she totally demeans me in front of other people and trys to snatch him away and do things for him instead of letting me as if i don't have a clue what i am doing. and just yesterday she basically put her foot down and told me that she would be the one getting his birthday cake this month. i mean c'mon this is his first birthday. that is a huge milestone that is more for the parents than anything but i really want to make it special for him. luckily i was strong enough to tell her no that i was getting the cake and i was so proud of myself for sticking up for myself but i just don't know how to approach sticking up for myself in the bigger picture. how do i get her to back off to where she actually does it but doesn't destroy our relationship in the process. please help.