In terms of power: Anything you get will have more than enough power to do anything you listed, and then some. Don't let advertisers fool you: in terms of the things you want to do, computers have been able to do that stuff without blinking an eye for a long time.
Just to give you an idea, my processor model (Athlon 64 3400+) is about two years old. I have literally dozens of programs open and about 20 different webpages, and my computer is using less than a *tenth* of its processor power.
Almost everything you can get will have wireless internet, and there's not that much difference between one brand of wireless internet and another. Don't be fooled by technologies that go by names like "Speed-Booster" and "Super-G" -- they don't do anything useful.
So, the only differences that really matter to you are battery life and the screen. The best way to learn about screens is to go to a Circuit City (not a Best Buy if you can help it -- they're not as willing to answer your questions without trying to sell you something, on average) and just look at them. Fiddle with the computers, and see what size you want.
On screens: Some laptops have a matte screen, while some have a glossy coating. Go look at both types, and see which you prefer.
Large laptops are actually a bit cheaper than small ones, so you're in luck. She may want something a bit smaller, though. Mine is 15.4", which I find to be a bit big on occasion. Just see what you like.
For battery life, don't trust the manufacturer's specifications, as they all overestimate by different amounts. Ask on the forums about a specific model, and people will help you out. Make sure that, whatever you get, it has either a "Turion 64" (not "Athlon 64"), "Pentium M", or "Athlon XP-M" processor -- those have the best battery life.
If you're getting a machine that's 15" or bigger, you want an 8-cell battery at least. Smaller machines might be able to get by on a 6-cell.
A machine with a 15.4" screen, a Pentium-M or Turion 64 processor, and an 8-cell battery should get you around 4 hours battery life, give or take.
Almost no laptop is going to come with those Microsoft Office programs preloaded on it. You'll have to either buy a copy ($300) or acquire one in some other way. HOWEVER, there's a great program called OpenOffice that you can download for free at www.openoffice.org
. It's fully compatible with Microsoft Office, and is basically equivalent; I actually find it to perform better. I used it throughout my undergraduate career (I'm in grad school now), and highly recommend it.