For all three of my pregnancies, my modest B went to a DD well before the babies were born. I didn't gain a lot of weight overall, and what I did was all babies and boobs. After I stopped nursing, it went away because it was just enlarged milk-ducts, not breast tissue or fat. I was lucky, they didn't flatten out like deflated balloons like some women get. If that had happened to me, I'd definitely have looked into trying to make them semi normal again.
If she is two months post partum and nursing in that photo, the size and shape are about right, but she isn't doing herself any favors by not wearing a properly supportive nursing bra.