AITA for not wanting to change the agreement I made with my sister
Hi, I'm a 21-year-old female, and my twin sister is the same. We bought a car when we were 18 and have been sharing it for the past three years, making it work with school and work. We had discussions about when we get another, and we both agreed that whoever put the most money into it would keep it. We were both fine with this. But about a week ago some family came to visit us. My mom and Grandpa were talking about looking for a car the next day. I asked my grandpa who they were getting a car for and he just brushed me off saying, " Don't worry about it” I obviously started thinking he was buying the car for us since he has been talking about it for years now. I told my sister that night, as we were talking about it she brought up who was going to get the car I reminded her that we already talked about this and that I would get the car since she got into an accident. The accident was not her fault. It was icy on the road, and she slid into a guardrail. After I reminded her of that, her entire mood changed and she got visibly upset. She went on about how there needs to be so many things done with the car like how we need to get the engine the tail light seal repaired and we had the car for so long and haven’t gotten any of the additional things you wanted to add to the car like getting the windows tinted Apple CarPlay, and a rear view camera. I tried to remind her that no matter where we get it, we’re going to have to put money into it to get it fixed up or add the things that I want to the car so we will both be spending money to get these cars fixed up also I could have been wrong that it wasn't for us. Turns out I was right the next day he my sister and one of my mom‘s cousins went out to look for cars. They didn’t find anything in the price range or anything that we would have wanted. They told us to continue looking for cars and that he’ll just send us the money for it. Later that night I’m looking at cars showing her them and everything seems fine then she gets upset saying I'm getting excited for a car that's not even mine then continues to complain about all the things that need to get fixed in the car and I am trying to remind her that I’m not getting the car tomorrow. She’s not hearing that she comes up with the idea of that maybe we can switch the cars every other week I thought that was stupid that makes no sense to me. She got mad that I said that and ignored me for an hour. Then she thinks about selling the current car we have so that she can buy a new car and split the money from it. I keep asking her whether it is really a problem that she keeps our current car she says no but wants us to share the new car I told her no the defeats the purpose of us both having a car. We keep going back and forth about the same disagreement because she wants me to follow what she wants so aita for not wanting to change our agreement?