I've read that kitty diarrhea and messes can be the result of worms. Anyway to can trap her and get a stool sample or take her to the vet?

Oh, is she a Manx? There is one at the shelter that has been there for years because of her diarrhea problem. She's always a mess but she can't control it. The tech there said that Manx are prone to this recessive gene.