I've tried searching for an answer to this question, but not sure what terms to use and I'm coming up empty.

I'm hosting a small site for a friend as an add-on domain. She wants write access to her folder, but I'd rather not let her have any access to the rest of my site.

Rather than going in and password protecting all my other directories, can I make just this directory available with a password, while leaving the others invisible?

thanks!

You can also specify directory permission of rad, write and edit as per the way you want to give her access. Remember some of the link exchange software which asks you to give notepad file  with 777 permission.