word press related post plugin

I installed this plugin and now when I try to log into my dashboard a get this error message “Fatal error: Call to undefined function is_site_admin() in”……then the plugin file……”on line 81.”

I am trying to find the file via Filezilla so I can disable but cannot find this plugin in the plugin folder.

What to do please?

ps I cannot access FTP via Godaddy right now as they have some problem.

thanks.