OK, University has disgorged this years graduates incl my son and his girlfriend who have now taken over my home and my broadband ( that's a medium fast internet connection to those of you in the colonies )

Girlfriend has a PC and it hogs the bandwidth as soon as it's switched on and I'm having very poor access from the other macs in the house. trouble is everytime my son or wife asks me to troubleshoot my connection the girlfriend swears she's not downloading anything or watching any streaming movies but she is connected, SHE'S ALWAYS CONNECTED !!!
I do know that if I pull the plug, wait 20 secs restart the router the connection problems resolve but soon slows to a stutter again and I had no trouble before they descended upon my little abode.
Apart from disbelieving her and challenging her is there any way I cam monitor whether or not she's Utorrenting or watching streaming movies, I don't want to pry as to what she's actually watching, it looks like vampire movies and innocent enough but I can't troubleshoot connection problems if she's telling me she's not downloading when she is.
My router homepage simply tells me she's connected but it doesn't have an option for monitoring how much bandwidth shes's using.
Peter