Well, without getting too heavy into the details of it, basically the positioning of the code that determines the color of the link is the issue. In the case of the earlier ones that turned purple when you clicked them, the color code was on the 'outside' of the link, which means it made the link itself that color. The last links you posted, the color coding is on the 'inside' of the link which actually colors the text of the link. I may seem weird like that, but a link can be colored and then have the proper behavior happen to it after it has been visited (ie: turning purple in this case) or the text of that link can be colored and the same behavior won't work since the text itself is basically hard coded to be a certain color.
For a link, you have two basic parts, the link itself, and the text that is displayed as the link. If you specify for the link to be a certain color, it will be like that, until you click it. After you click it, it resorts to whatever the normal behavior of a clicked link is in your browser. If you choose to make the text of the link a certain color, it bypasses this behavior and stays that color always. Make sense? Bit confusing maybe, but that is the basics of it. I suspect when she was making that webpage, since the default color of links is blue in most editors, she may not have manually highlighted the text of each link and specifically changed it to blue, which would cause this behavior.