I appreciate your response– I’ll show this to someone outside our department who may be able to help us do this.
I could have just as easily made the mistake that my co-worker did… honestly, we’re just not web design/HTML savvy. I wouldn’t think that simply previewing a different/new theme would lock us out from our administrative dashboard and make the site unviewable. I think it would be better for us to have a tumblelog as a website to make it more foolproof. I don’t even know how to do what you suggested in order to fix it (but still so appreciative, because again, we’ll defer to someone who knows more and will hopefully help us).
Any other tips are helpful for us hopelessly hopeless!