Just out of curiousity, are you putting this capture device between the pfsense box and the modem, between the switch and your daughters computer, running a hub for your daughters computer, or spanning the switch port of your daughters computer?
The cheapest solution that I can see by far provided you don't need over 10Mbit is to get a cheap tiny hub, connect it between the wrap switch and your daughters computer, and instead of running a proxy just have the capture device in promiscuous mode to capture everything travelling though that hub.
At my last job we had an IDS and it was basically connected to a switch with a spanned port. The port that was being spanned was the port of the default gateway.