I have a 12" PowerBook sitting right next to me at this moment. It used to be a friend of mine's but he broke the power connector off inside the port, and his folks got him a new MacBook.
After fixing it and reinstalling apps and all that, here is what I have to offer
The keyboard is really nice. I stand by any previous statements I have had regarding the quality of Apple's keyboards. They all feel fantastic. I am a little more used to my MacBook's chiclet style, but typing on the PowerBook is not difficult by any stretch of the imagination.
The trackpad is tiny! The best way to compare the two is like this. Do you have an ipod (full ipod, preferably a video)? Set it down in front of you sideways, and now you know how big the MacBook's trackpad is. That is what I have been using for the past 15 months. Now, cut your ipod in half, and re-orient it to the vertical.... that is the size of the PowerBook's trackpad. Also, 2 finger right clicking required third party software, as does 2 finger scrolling (unless you get a last generation 1.5GHz PowerBook)
Compared to my MacBook it is slow, and the processor quickly jumps to 100% load. That doesn't mean it really slows down much, or anything like that, OS X does a magnificent job of handling itself in such an event, but after being on my system where only 720P video, or DVD ripping would spike my CPU meter to max, it is a little disconcerting (so, your sister would never even notice)
It is a PPC, so if you get her a copy of Office 04, it will run quite smoothly on there since it is a PPC app. Leopard runs like a dream on the 1GHz with 768MB RAM and I would expect that it would be ok on 512MB RAM as well.
Upgrades for this thing are expensive though. The older PPC Macs were quite picky about their RAM I am told, and the Apple certified RAM on Newegg is $100 for a 1GB stick (the PowerBook has 256MB onboard and only 1 RAM slot, maximum of 1.25... actually, I think the 1.5GHz model had 512MB onboard, so 1.5GB max) and it uses ATA hard drives. Those aren't that expensive, but replacing the hard drive requires you to remove about 20+ screws, and in the process possibly severely damaging your power button connector. They did not make this thing technician friendly.
Don't let me give you the idea that this would be a bad purchase however! Not in the least. It is plenty powerful in it s own right, has a really nice, easy to read screen (1024*768 resolution), great keyboard, is really small, looks great, and is built solid. Plus with a fresh battery in there, you can expect to get 4 hours or more of battery life.
Oh, and if you do decide to pull the trigger, I have a 512MB stick of Apple-pulled RAM laying around that I could sell you... Heck, I could sell you this PowerBook
