Is she giving unwanted advide or saying things like, "Well, I wouldn't have done that." yeh know...
I worked with people like that and they were very annoying. I blew them off. I just had to tell myself they're unhappy and they are taking it out on me.
One time it got to me though, and here was the scenario:
Me:"I don't like to dress my daughter up in tons of clothes while we're in the house."
Coworker: "Oh my, she must be soo cold. I know I'm cold and I'm 54! My grandkids get cold in this weather"
Me: "Oh wow your house must be freezing! My goodness if they're cold you should really dress them warmer!"
I basically did it back to her. Might not be the most mature way but it made me feel better