Try another browser (Chrome, Firefox, Opera etc).
If she has extensions installed disable them in Safari's preferences > Extensions tab.
You can also try resetting Safari to remove all cached data & history.
Safari > Reset Safari is where you do that.
You need to provide more info stating what exactly happens - any error messages, dialogs or blank pages etc. What else is different about the other Mac - What OS X version? What Safari version? Get those from the 'Safari menu > About Safari' and 'Apple menu > about this Mac'.
You can also contact the site about your issue - they may be able to help.