Dark Green Stool

Dark green stools can happen when baby's digesting breastmilk a bit differently, especially thawed frozen milk, and it's usually nothing to worry about as long as she's acting normal and gaining weight okay. That said, since you've noticed the pattern with the thawed milk specifically, it might be good to bring her to see the PD just to rule out anything, and they can also advise if there's anything about storing or handling the expressed milk that could make a difference. In the meantime, keep an eye on her wet and dirty nappies, feeding cues, and how she's settling after feeds.