how is your network set up?
If net to router to PCs then chech your router for bandwidth limiting features. If the net is hooked up to your PC then when she hoggs it, just disable ICS on her -she will learn to share.
One thing I did when i had a bandwidth P2P happy mate was to set my PC as a DMZ in the router (all ports forwarded to me) and the use a soft firewall on my PC. That made it impossible for him to achieve fast P2P transfers.
I wouldn't suggest sneaker measures like this but it seems you have tried talking and reasoning with her. If you have a router then see if the router has any bandwidth limiting features and use them.
This article may be of some help to you. It is about disabling bandwidth limiting but im sure you could use it as a reference to limit her bandwidth