Laptops are generally divided into these categories:
1) Light - 12.1" screens and 2-3 lbs
2) Medium - 14.1" screens and 4-5 lbs
3) Heavy - 15 - 15.4" screens and 6.5-7.5 lbs
4) Desktop Replacements - 15" - 17" screens and 8 lbs+
Of course the bigger you go, the better the deal (slim components are very expensive). Some of the desktop replacements are rather thick and use desktop parts. Based on your description, I'd probably want to go to some store to check out the difference between the mediums and the heavy laptops, to see if she cares. 2-3 lbs doesnt look much on paper, but its pretty signficant for a laptop.
But from what you're describing, I'd get an IBM T40. Quality build and weighing in at ~4 lbs with a 14.1" screen and should be had for $1400.