Ok, if your main pc and laptop are both on XP just open the network connections folder and run the network connection wizard from the Setup a Home or Small Office network.
This will make a shared folder on both pcs, right click on it or any other folder that you want to share and tick the Make this folder available to other users on my network and also the box Allow other network users to alter my files.
Then you just open network places on the pc that you want to copy files to and provided the folder is set to be shared on the other pc and has the correct permissions set for the files you want to copy, browse for the folder and drag them across.
She will only be able to see your emails if you set your email account up on the laptop. If you did that then whichever pc downloaded the mail first would have it. The best way would be just to have your mail account on your pc and set a different one up on the laptop for her to use