Another User Screwed my Wordpress site! Slow, unresponsive, conflicting plugins etc

Another user was given access to my wordpress site to fix 1 error that was occurring on a specific page. This was a small fix and was told it would be easy to get done in under 1 hour. Instead this user created other issues which eventually caused our site to be unresonsive for several hours. Since yesterday we currently have the following issues; 1. The website is displaying an older version of the site (changes that were made in the past month are not visible). The current version is showing when i log in to make edits in the admin section but not to other people from different computers/locations. Cache plugin has been cleared with no avail. 2. Our load time for the site was 2-5 seconds, it is now over 10 seconds to load and for some users it does not load at all! 3. Certain plugins are conflicting with each other causing some pages to give a "500 error" or "Unknown: Cannot use output buffering in output buffering display handlers in Unknown on line 0" 4. For some users the site will not load and will provide an error "Error too many redirects" I am looking for someone who has the experience AND patience to go through and have our site working back to normal with all plugins, pages and site speed up to standard. I DO NOT want a user who will just do a few tweaks and then say "oh well it is working on my end just check with your hosting provider" I have contacted our hosting provider since the user caused these issues and they have assured me this was caused via wordpress or cpanel changes made incorrectly. Domain name and email is with "Network Solutions" Hosting/cpanel is with "Host Gator"