Hi
@JuneM
This is an old post, so likely the OP will not respond since they have not been on since 2013.
Photos of your hen would be good.
Walking around with her bottom almost on the ground sounds like she has a reproductive problem. Internal Laying, Salpingitis, Egg Yolk Peritonitis, Ascites, cancer or tumors all have similar symptoms and can make the abdomen swollen and heavy.
When you feel the abdomen is it hard, fluid filled, etc.? Sometimes if there is fluid in the abdomen it can be drained to give some relief, but that should only be done if the hen is in distress or having difficulties moving about.
A hen that has these problems can go for quite a while. IF she is eating/drinking normally, fairly active, interacting with the flock then I would be inclined to leave her be.
Check her regularly for lice/mites and see that her crop is emptying overnight.
Look forward to your photos