Hello Nick,
If you delete both plugins from your client’s plugins directory then the site will definitely work now.
Please check the troubleshooting section of the documentation for more information on what to do in this situation. Check the section “When I activate the plugin, my WordPress becomes extremely slow and is unusable.”.
If you need to diagnose the problem you might need to enable debugging and check the logs. If you see any errors in the logs, please send them to me or post them here.
Hope this helps.
kind regards