Now, I need to explain a feature of Internet Explorer 11. It has a feature that allows it to run webpages as an older version on IE. For example, I can say hey IE 11, I want you to run as if you were ie 7/8/9/10. This feature was built in so if an organization had a legacy application built and it was mission critical their IT team could set the web browser to render pages as whatever version of IE was needed to run it. This feature is called Document Mode.
The only way I could get the page to look the way it did in the screenshot was to change my IE11 document mode to IE7. This is intentionally telling IE to run the page as if it was IE7. IE7 was built and released in 2005 and as you can imagine the site was not built (nor should it have been) built for support for IE7.
At this point the most reasonable explanation is that the affected user or users (especially if part of a large organization that has full control of their PCs) have had their Document mode changed. Possibly from their IT team in some kind of network setting or other reason.
The quickest way to find this out is when the page is loaded on IE 11, have the user click on the "f12" key. This will open a window. You will want to make sure you are on the "Emulation" tab in the black bar on the top. Then you will see Document Mode Drop down box. https://share.getcloudapp.com/X6u2wmn0 This box should say 11. If it says 10/9/8/7, then it has been set to render websites at that level.
Unfortunately, this is an IT / machine level setting. There is no way for us to read/override/reset this setting on someones computer. They will either need to change the setting them self, or let their IT team know that this is happening within their organization so they can fix it.