If she is using ZoneAlarm as she says (especially if she paid for the "Pro" version), there is no reason to turn on the less capable Microsoft firewall in XP. There is something to be said about a product that not only lock others out and make you "invisible" as well as warn you when applications (or trojans) try to access the Internet behind your back. Of course, all of these products also need to be kept up to date and are not worth much if one doesn't!
--
The most expensive tool is the one you buy "cheaply" and often...