You can use Flubenvet in her feed to worm her if you wish. Panacur horse paste is also available in the UK and can be used to worm at a dosage of 0.25 ml per pound of weight given for 5 consecutive days. But wait until she has stopped molting and all feathers are grown in to use Panacur (fenbendazole) since it can affect feather growth. You may want to weigh her to get a baseline weight to know if she is gaining or losing. Scrambled egg, wet mushy feed, and tuna can be used to help her gain. Cancer, which is sometimes common in hens over 2, can be a reason for severe weight loss. Also check her crop in early morning before she has eaten to make sure that it is emptying normally. If it isn’t and she has a crop disorder, that can be another reason for weight loss.