Anxiety about MIL 😤😔

I'm due October 20th with a baby boy. Our rainbow baby to be specific. Well my MIL is an alcoholic & not only that but LOVES & FEEDS off of drama. We were so close but now it's changing as I approach my due date & see her for who she really is. She has basically taken over the mother role for my 1 year old nephew and has been since the day he was born because my SIL has let it happen & the baby's father has never been involved. My MIL thinks I'll be the same way. That the baby will always be over at their house or something, she always says I'll get tired of the baby & drop him off. Mind you I have a 8yo daughter that I was a single mom to for 5 years until I met her Son, my now Fiancé. I never had help from anyone, I got my own apartment and cared for my daughter all on my own provided day care so I could work etc. all at the age of 18. So why does she think that I'll be different  with my son?? My hubby backs me up and tells her that's not how it's going to be but I don't know why I'm so stressed about it. I know she'll play the victim card whenever she asks for the baby and I say no. I will be a stay at home mom once our son is here. She also says things that bothers me like I can't discipline him or she'll be mad at me, that when she has the baby its her time & she'll do whatever she wants & I don't have a say, or I can't take my own son places that she doesn't agree with because he'll be little. WTF. Other things too that I can't think of right at this moment. But I do not like how she cares for my nephew & that's not how I want her to be with my son when she is around. She will be his grandma & nothing more. I just hate that she'll make everything about her and TRUST me she will. It's like walking on eggshells around her and I don't want that energy around my son when he's here. For instance, when she's mad at my SIL she talks badly and calls her names with profanity included in front of my nephew!! His own mother! Why would I want my son alone with her especially since she drinks? My hubby is seriously the odd ball in his fam.. He says not to worry and yea maybe I shouldn't but I cannot help it. It's like it'll never be a normal grandma grandson relationship which really sucks because I'm a very family oriented person. I just feel stuck and have no idea how to handle it. 

Sorry for the excessive BS 😭