so, I'm guessing you have a setup as follows: DSL Router -> hub (your PC plugged into one port, wireless modem/router) plugged into another and her connecting to the modem/router? Or, do you have a DSL Router w/ built in Wireless that you are using? If you just have a wired DSL router connected to a hub that you connect to, then someone would have to be, to my knowledge at least, running cable getting into your wired router. I'm not aware of a way to steal DSL w/out killing the other router since the DSLAM wouldn't authenticate w/multiple routers...
Xbox360 / PSN / Game Center / Steam: yawmush