Am I wrong for this?

I watch my niece so my sister can work. I already told her to make sure she has back up because I can go into labor anytime (I’m 36 weeks tomorrow). I plan on staying in the hospital with the baby until I’m released which is usually 2 to 3 days, because I want to enjoy the baby before I go home. I also wanted to tell her that I want her to find back up for at least a month from the time I have the baby. I will be very tired and I’m also going to be exclusively breast feeding. I had my last child 4 years ago so it’s like starting all over. I just honestly can’t see myself bringing my baby home and watching my niece also. I don’t know how to bring this up to her. I feel like because this is my 3rd child she’s also going to think I can just take on watching her child while I have a new baby at home right after I get out of the hospital. Am I wrong for this? Or is this okay? And if its okay how can my fiancé also decline on watching my niece because I know for a fact she will ask him which means my niece will still be here at our house and I don’t think he should have to take that responsibility plus I’m going to need his help myself.