DD-WRT and Tomato have versions that include VPN server. If her home router will run one of them, it's pretty easy to set up. Both firmwares support PPTP VPN (the kind built in to Windows and everything else). Tomato also supports OpenVPN (a more secure, SSL based VPN solution).

I use a PPTP VPN on my iPhone and laptop for when I'm traveling and want to access my home network.

Happy to help with configuration if needed.