Thank you for rescuing her! We saved 4 kittens in our backyard this September and kept all 4. They were about 4 weeks old too and we're abandoned apparently because they had not eaten in days. They were malnourished and weak. I handfed them with syringes for weeks before they became weaned. They won't poo if there's nothing in them, that's how our 4 were too. They didn't go poo for days on end & I was getting so worried but then it occurred to me that since they were malnourished everything wasn't working right. Once they became stronger they started to go. Praying you find her a good forever home!!?