The droppings are not normal. I've lost birds to reproductive problems even once they were past the age of laying at all, it's always possible. Too many treats can make a bird fat, which can contribute to all sorts of health problems. It's often difficult to know until they pass and a necropsy is done, symptoms can be very similar between different causes. How is her weight? Is the breast well muscled, or is the keel bone very pronounced? Check her crop, is it full, empty, soft & squishy, hard, etc? Check again first thing in the morning before she has access to food or water, it should be empty then. Have you ever wormed your birds or had a fecal test done to check for internal parasites?