I raise s silkies and in my experience silkies can go off there lay for lots of little reasons. if they are moved around or bothered or just not comfortable they can go off lay . also if they are not feeling well. sometimes when pullets first come into lay they are not regular yet.my pullet just came into lay two months ago she laid two eggs then nothing last month then I got an egg four days ago then nothing else yet. I think when they first start to lay its not a real regular thing until there bodies get used to it. this could be what's happening. but the black poo would have me concerned too. does it look like old blood? are you certain she didn't eat any berries or anything to stain the poo.worst case could be old blood from inside her from something. hopefully not. keep a close watch on her for ANY other symptoms. is her abdomen normal? no swelling or any thing like that? just watch her. she's eating And Drinking Normally Right? Not Losing Any Weight? IF you notice any other symptoms then it could be cause for concern. right now I'd just keep a close eye on her. she could have ate something that changed the color of her feces. I wish you the best of luck. hopefully she will return to normal soon. I hope this was helpful in some way.