They can be anywhere. If you can get into Outlook, right click her personal folders file, and somewhere in there (I don't have it in front of me) it will give you the location of the file. It doesn't necessarily have to be on the local machine, it could be on your network.
Unless . . . (apologies if I'm being stoopidly obvious) in fact it's not a set of personal folders, and is actually an exchange mailbox. Then it would be on the server, and you don't need to do anything with it.