So, for clarification, you picked up all of these birds 2 weeks ago, from some one who had ALL of them for the 15 weeks prior, and they have all lived together for the last 17 weeks? As PP have stated, give her a thorough examination. But, before you do, pick up one of the others of about the same size, and palpate her, so you have a sense of what "normal" should feel like. Feel around particularly to see if she has any swelling in her abdomen. Look for mites and lice, check her vent, under wings, nape of neck. What are you feeding? YOu could give her 1/4 of a tums ground and dissolved in a bit of water, then mixed with a bit of bread. I am not qualified to recommend calcium dosing, but I would feel comfortable giving that amount to one of my birds. You might do some google sleuthing to see what the recommended dose of calcium for an egg bound bird might be.