Any way to disable full screen apps?

Hello,

My grandmother has had a Mac for a while now, even though she has no idea what she's doing with the thing. Whenever I fix her computer, she's got nearly a million windows open, she's dragged random web images onto her desktop, and she thinks that applications have been deleted simply because she accidentally removed them from her dock.

In short, she's the stereotypical elderly technology user.

Recently, I spent nearly an hour on the phone with her as she tried to describe how she couldn't get to her email, but "the google was working fine." Finally, I figured out that she had somehow managed to send Safari into fullscreen mode and couldn't get out of it. I told her to simply press the escape key, and if she remembers this, it should work for her in the future.

But, I was wondering if anyone knows of a way to permanently disable the possibility to fullscreen applications. It's not of much use to her, and I anticipate that she'll face this problem in the future.

(Also, I don't mean to come off as ageist. She's a very sweet woman, but technology isn't her forté.)