<human>: Can you give me the gist of the text in a nutshell?

I should start by noting this isn't a fear of him cheating on me with her, I don't know how to describe why, but if you look at the dynamics of their relationship, you'd probably agree with me. 

I've told him of my discontent with her, and that I don't want to prevent him from being friends with people. The problem is coming though, because I don't want her at our wedding, and I don't know how much longer I can prevent myself from going off on her.

Everything she ever says to either one of us is how we are doing things wrong, and how she's doing something right. How great and advanced her son is, and how mediocre ours is. Basically, her life and choices are always better than ours. 

It's always depicted as concern, but it's cattiness (which could alsobe my much needed rant her, sorry). 
Ex: when our son was a few months old, I was breastfeeding and working a crazy schedule, so we coslept. She had to chime in and tell me how bad that was, how it might screw him up psychologically and how she's just worried for him because her little sister visitor until six years old. When she had her son she never breastfed (something she scolded me for because she assumed I would never do) because it was give her gross breasts, and at 8 months he has been cosleeping since day one.

It's just little judgemental things that keep getting under my skin. I try not talk to her so that's either why she's doing this or she's doing it just because. My fiance said she's done this stuff the entire time he's known her (middle school) and she just doesn't know. 

Can I say something to her without it causing an argument between her and my fiance or my fiance and me?
<bot>: it's not a concern with them having an affair. She's always being hypocritical and giving me masked insults. I try not to avoid her so maybe that's why. How to I stop this before I flip?