The machine is running XP... not Pro but whatever came with this Compaq (I don't really remember the variants of XP that they offered ... is Home the only other option?)
I have experience using Remote Desktop and VNC (usually install TightVNC) but I've never actually opened up a home desktop before (I've used SSH tunnels and cygwin to get to work PCs via a gateway SSH server so security of the Gateway has always been handled by someone else). And I've done port forwarding for p2p apps before on home machines.
My preference for its performance is usually RDP but I don't know if one of the above is more recommended than another, or even some other option altogether.
Also related to this is suggestions on configuring her PC's networking to give it access... it's sititng behind a ZyXEL P-330W router and uses DHCP; presumably I need a static IP address to properly port forward to that computer always. I don't believe the ZyXEL allows you to always give out a known IP address via DHCP based on a MAC address, but I could be wrong about that. I can assign a static IP address but just have some concern should the router hardware ever be replaced and/or the Cable Modem provider's DNS servers change (wish XP had a "static IP / DNS from DHCP" option). My thought would be to give it a static IP on the NAT subnet and use OpenDNS's DNS server IPs, but I'm sure there are other options that I'm unaware of for that.
The ZyXEL does support a DynDNS account though so I should at least be able to find the router independent of the cable modem IP at least.
Thanks for the help!