I would also recommend not giving them additional grit if they are foraging around. The grit sitting in her belly bothers me too. They don't get additional grit and I'm sure it would have been worse if they did.
Watch the plastic with the chickens too. My barred rock is pecking and shredding the flap door for the coop. So that has to go now because she is obsessed with it.
We buried an old boat and fill with water for my ducks to swim in. The whole front hull underneath had a styrofoam liner. I could hear them nibbling on it (drove my dog absolutely crazy! Like fingernails on a chalkboard) lol. Eventually they broke it loose and a big section fell out. When i picked up the chunk that was left, it was pretty obvious they had probably ingested some. Apparently they pooped it back out, as I never had any issues.