Custom CSS not displaying on client's computer

We are having an odd issue with Catch Everest, and I am running out of things to try. I implemented this theme several months ago, and used the Custom CSS box to customize it. This has worked just fine until the WP update. Suddenly, we could not see the site on any computer in her home. I could see it on mine, and she could view it on her tablet, but the site wouldn't do anything - just displayed a link to the cgi-bin folder. I did some research, and found that resetting the Permalinks should fix the issue (probably due to .htaccess file being overwritten during update.) I did so, and now she can see the site. However, the custom CSS is not loading for her now. I have reset the Permalinks once again, and also changed the theme and changed it back. I am waiting for a response from her to see if that fixes the issue. However, I was wondering if anyone else has encountered a similar problem, and how did you fix it? I think that the problem is that her antivirus is somehow preventing the code from loading properly - and if she is having that issue, so are visitors to her site.