Mil doesn't understand my choice to bf

My mil is having a hard time understanding my desire to try to breastfeed. I will be a ftm in February and I am so excited to try to breastfeed! I decided that the best way to try is to make a commitment to it. Yes, I have extra bottles and formula in case it doesn't work, but I also have been reading books by la Leche league and ordered a pump through my insurance. My mil told me the other day that with the baby coming I am going to need "a lot of bottles". I know that she didn't breastfeed at all. I told her that I have about 6 or so bottles to start out with, but I am planning on breastfeeding, and she gave me the most shocked face I have ever seen. She was almost offended and trying to hide it. After staring at me for what felt like an hour, she looked at my wide eyed and nodded her head slowly taking long nods up and down. Is it a generational thing? I don't understand why she would assume that. Maybe she really wants me to do things the way she did, which I hate. Maybe people used formula in the early 80's? My mom breastfed me and my sister so Idk