I'm afraid I'm turning into a Bad person?

I was my grandmother home.. and she said something about health problems that she has had.. and I'm trying to say this nicely but she is on the heavy side and she's 80 years old. So, I suggested to maybe try to eat healthier and see if things improve.. Also, my mother NEVER liked her.. but the reason is my grandmother is a liar.. but my mom is also. I don't want to take sides. Because my mother is a very hateful person.. but I agree with her on this. Well, my grandmother mistook what I said for calling her fat and not humble at all... I never said that! I also told her that I wasn't calling her fat even though she really is. Weirdest thing of all.... She said that I wasn't humble! I never said that. So, as I dropped her off with my dad, she tells him! Clearly, my dad can't punish me anymore but he said some pretty hateful words to me. Like if you were in my house I'd kill you for talking to her like that!! I just stayed quiet for a while. This really has been upsetting me because I never liked my mother but for a first. she was right.. What should I do now? I feel awful that she actually thought I'd be hateful and rude. I barely even talked to her! It was like a 5 minute drive!