Hi @Mariette_Barnes and thanks for reaching out on the Forum!
I can see that Cheryl shares the same email domain than the rest of your colleagues, so I guess she is a member of your company, an I correct?
In Asana, anyone sharing your email domain (ie: @mycompany.com) can automatically join your Organization (when they do, you will see their name in the Assignee drop-down menu). you can learn more about this in the following article: https://asana.com/guide/help/organizations/basics
From what I can see on your screenshot you’re the only member of this project (https://asana.com/guide/help/projects/people), so Cheryl definitely can’t access it, no worries there! However if you’re working for a large company, I would recommend adjusting your Team permissions to make sure taht only your team members can access your projects!
Hope this helps Mariette! Please note that I’ve edited your screenshot to hide email addresses and protect your colleagues identity! Hope that’s ok