Macs are great. I have an iBook that I use for general sofa-based surfing and work and I travel with, as well as my Windows gaming rig.
For a start, they're excellent for people who don't have the knowledge or the inclination to acquire the knowledge to keep patched and free of crud: there are no trojans or viruses or any nasties for Macs (though they can pass on Office-based viruses). For another start, they ship with some superb applications - many have AppleWorks, they all have iPhoto, iTunes and a Mac with a burner will also have iDVD. And it comes with a superb email client, too.
They're easy to get to grips with and they just blinking work - straight out of the box. They all ship now with Airport Express cards and connect up to your wifi network without making a fuss. They're rock-solid, too: my iBook is 18 months old and hasn't once crashed on me.
If you've got an old monitor, keyboard and mouse lurking around, get her a Mini (put a bit more Ram in it, though); otherwise I think the iMac range is excellent and I always recommend Macs to people who don't know - and don't want to know - much about computers. If I weren't a gamer I'd have an iMac myself.
Even the bleat about software not being available is less of a problem, plus there is plenty of free cross-platform software: OpenOffice and Nvu for starters.
Don't dissuade her. Let her persuade you - you might enjoy having a new OS to play with.