So if having a photo of yourself, doing something you're proud of, featured on a magazine cover is showing off, then all
those fishermen that feature on "Carp Fishers Weekly" are just SUCH divas! How dare they flaunt their enormous catches at the world? They might make the other fisher-folk jealous!
If every woman lived in that "half way house", (like the good, sweet, modest, self-deprecating lady she ought to be) then we'd never see media images of women doing anything other than modelling. Breast feeding is something women do. Mothering is something women do. Feeling PROUD of those two things is NOT something that women commonly feel able to express to their friends, let alone the world.
Some women have the guts to make a statement about something they feel good about. It's not something we see very often in our culture, but it does happen. Women are often the under sung overachievers.
I can guarantee if that image was of a man doing some epic fathering, we'd all be bloody cooing over him 
What are media images of women meant to represent us as doing exactly?
Something more socially acceptable maybe? Something more typically "feminine"? Like what?
This woman is being assertive. Get over it.