She's nursing.
Btw, during her first pregnancy, her tits got pretty big, but they deflated when she was done nursing, so she got a breast fat transfer procedure done to fill them back up, and they ended up being permanently close to the same size as they'd been while she was nursing.
Now that she's nursing again, this time combined with all that extra fat from the fat transfer, her tits have gotten absolutely insanely massive, as you can see. Hopefully when she's done nursing she'll do the same thing again, so they'll stay this size forever.