Consider keeping her up during worm treatment, or her poo could recontaminate her pasture. If the top of her tail is itchy, sooth it with Listerine and baby oil. Good look! Oh, and we all like a good picture. Come on, now!
I am not 100% sure but I thought that there was a sickness that horses can get from coming into contact with possum/racoon poop.One of the early signs was a certain way the top of the butt/hips of the horse slopes and another sign was if the tail is stiff ....and then it continues on to be something with the nerve system...Just a thought
My old welsh pony had a big belly and was skinny up by her rids and hips. She had cushings(sp) and than she coliced really bad so we had to put her down.
Either a hay belly or worms. Hay belly is if she is eating poor quality hay and it sits in the belly much longer trying to soak up all the nutrients. Pregnancy could be it too, you would check for a milk vein pertruding down the side of her belly and a filled bag.