Xandros and SimplyMepis both fit the bill, you can get the system up and going in about a 1/2 hour. If she has a high speed connection, you can update/add programs quickly using Xandos Network or Synaptics Mepis, another 1/2 hour.
By user friendly I mean close to Windows apperance wise and something that won't crash a lot (error messages give her goosebumps).
One last thing, I get your last point, but I don't have a lot of time to set something up correctly like Slackware, or otherwise I wouldn't have posted this. I'm really busy and work on Saturdays, I live in Chicago and mom's in a indianapolis suburb. So something that wouldn't take much time to install or configure would be nice too.