Doc E, Please help!

She does very good with her obediance as long as she's on a leash. As soon as I take her off the leash, she turns into an idiot! I can't get her to come, sit, heel, nothing. As soon as I put her back on the leash, she's good again. I even bought a 50' rope that I can use as a long leash. She does fine on that too. I can sit her and walk to the end of the rope, behind the house, and she'll sit until I call her and come right to me. Do I just need to spend more time working her on the leash/rope? Or am I doing something wrong?

Thanks for all the help so far!