I hear you. And don't really try to reason with her anymore. I try to let things go, but some things really get to me. Example:

Last month I sent her my most recent picture. She looked at the picture as said I look nice. On the next day she calls me and says: "I was analyzing your picture. I think you are pregnant and you're not telling me. You didn't gain weight because your face is not fat, but your belly is protruding and therefore you must be pregnant. I discussed this picture with your aunt and she agrees with me that you look like you might be pregnant". I told her that I am most definitely not pregnant. Her response was that even if I was pregnant I wouldn't have told her.

Although we didn't have a fight and it wasn't a big deal, I felt bad after that conversation because
1. even my mother thinks that I look pregnant, therefore I must be fat (I did gain weight actually, thank you for noticing)
2. my mother thinks that I wouldn't have told her in case of my pregnancy

What I am trying to say is that her way of intervening is upsetting me. I can indeed use the advice above and respond with a neutral phrases to the things she is saying. I think I am doing that most of the time now actually.