The key to making the meat tender is cooking at low temperatures. If you let your old soup hen come to a rolling boil, you made it too hot, and the meat will be tough.
This article from the heritage breeds site is a must read.
http://www.albc-usa.org/documents/cookingwheritagechicken.pdf
This article from the heritage breeds site is a must read.
http://www.albc-usa.org/documents/cookingwheritagechicken.pdf