Mil rant

My fiance is a mamas boy. And his mom has been coming to help like once or twice a week with our newborn. Which I appreciate but he's almost 2 months and I think it's a little bit too much. She has a controlling personality. My fiance says she's sensitive. There's just been things here and there that have been bugging me. She always has an opinion, and she always has to have the last word. I've let stuff go. I asked him to address those things with her because then if I do it. I'll look like a bitch and she might now stop. Anyways. I think today I have had about enough. And it was the smallest thing. She asked me if I wanted to sit in a specific chair because the baby liked it. I said no thank you and walked around with him. I come back and she moved almost like forcing me to sit there. I sat somewhere else and I asked her if she moved because she felt like I didn't want her to move and I was being polite. She said no. It was because she thought it was best for the baby. I told her she didn't have to move on my account that she can go back because I did not want to sit there. And she repeated why again. I let her know politely that when I say no that it means no. (Weeks before she has not taken me saying no thank you to likely, always repeating, are you sure? And giving her reasons why like she knows better) . So my fiance comes out and asks what's wrong. I let him know. I speak with him later and he says I probably hurt her feelings and my tone was wrong and that she was just trying to help and be nice. I told him i understand but i wanted her to know that I didnt want to do that and she can go be comfy.

And he says hes going to talk to her about it. I want to tell him I dont think he should because he told me to handle how I felt and it's between us. And his mom will let him know if it bothered her. I feel that way because now whatever I say is not justified and she will continue. But idk if I'm in the wrong. I probably am for waiting too long or for just not simply saying no thank yous once and ignoring it. I'm not sure how to handle this at this point.