I hate browsers that do these things automatically. But if your browser is really calling up 7-zip or some other process, maybe Chrome for example has a built-in decompressor for rars now or an extension that provides one, then it should be fine as well. As long as what you are looking at and placing into Mods\Packages is really a package file and not a rar (or zip, or 7z) file. And still no rabbit hole rugs showing up where expected in Build/Buy? Do any of her other rabbit hole rugs work out?
Can you try using a different browser to download?