Buy the latest greatest now, no sense of waiting for the next best thing if she will only be using the basics. The only reason whe would want to wait is if she will need some serious hardware components. But if only to surf, write, compose, watch movies, and play whatever get the ibook now. Or PB if she wants the extra hard drive space and vram.
If she doesn't follow the mac waves of new product, she won't know if there are new Ibooks anounced. Oh, and make sure you add min of 512 ram to whatever she decides from.