Some routers allow to bandwidth management,
You could set up a lower bandwidth for the lan, (her) and connect yourself with the wifi if possible.
another option, would be to use the word/web filter of the modem/router and lock some words such as torrents, tracker, announce, bit... It might help...
The last option would be to have 2 network cards and your computer, one connected to the internet and another connected to her computer.
Your computer would be sharing the internet with her, and with a software like Bandwith manager, you should be able to control her internet usage. The bad side is that your computer must be on for her to connect the internet...