Apple remote desktop is going to be your best bet for now, if you're looking for minimal setup. If you don't want to spend much money, you could set up a VNC server on her machine, and use a VNC client on your end to control it.
To enable VNC server on her machine:
-System Preferences - Sharing
-Check box next to Apple Remote Desktop
-A new box will pop up with access privelleges and other settings. Adjust your mom's settings there, and make sure you write down the password you set for taking control of the screen.
-You'll need to access her router settings and first set up her machine's MAC address to ALWAYS receive (static) the same local IP address from the router.
-While stile in the router's configuration, you'll need to access the port-forwarding area, and forward ports 3283 and 5900 (BOTH TCP and UDP, BOTH Public and Private) to the local IP address you specified for her machine.
-Next you'll need to download a VNC Client application such as Chicken of the VNC on your machine, and set it up using her networks EXTERNAL IP address to access her network. To find her IP address, use her machine to go to
www.whatsmyip.org, and type the IP it gives you into your Chicken of the VNC setup.
You should be able to log into her machine now and control the screen.
If you need any other help, let me know.
FYI, with the release of Leopard comes the new version of iChat. This version allows desktop sharing, and will negate the need for the above instructions, as long as you BOTH continue to use Macs (VNC server/client allows a mac machine to control a windows machine and vice-versa) and you BOTH upgrade to Leopard when you want to use it this way.
