I have been using the latest version of GoToAssist Express Beta for the past 8 months and have been very happy with it. It is free, for now, and the functionality couldn't be easier. The "customer" (your mom) goes to a web site, enters a 9 digit number and then you are connected. I'm not sure if they are planning on charging for it as it comes out of beta or not. If they do I'll be back in the market for a freebie.

At my old company we used a VNC package plus a relay server that allowed us to not have to open up any special ports on firewalls. That was particularly helpful to us but I didn't bother setting it back up when I left that job since I got the other freebie.

TeamViewer doesn't look all that bad from the web page, but I have no direct experience with it.