The growing bulge probably means she is egg bound which happens when she cannot produce the hard shell necessary to pass an egg. However, egg bound chickens generally walk like penguins and droop their tail. You may have caught it before these symptoms come into play, which is good. Give her a warm bath in water with epsom salt. You will be surprised at how she complies. Feed her a calcium supplement, one meant for humans is ok, and see how she does. Although the bulge may be something else, this procedure won't hurt, and when you know for sure it may be too late. I lost a hen to this issue just a few weeks ago. Wish I had caught it when she was at the point yours is.
