German shepherd weight and yard training

Question
I have a one year old female german shepherd that weighs 65 pounds. Her parents were both large breeds. She is small and skinny to me and anyone who sees her. Will she grow more? Is there something that I can safely supplement her diet with to encourage weight gain? How can I train her and my eight year old male golden retriever to eliminate in a certain area of the yard?

Answer
She should continue to fill out, so I wouldnt worry about the weight,  most GSDs look gangly at this stage.  

About the toilet.  You need something to define it from any other area in the yard.  Use a sindpit, or enclose it somehow,  just so it looks different. Then take them there to use the toilet and praise and give treats.