"Windows is done". What a final statement. PC sales may be mostly done. A desktop that was bought 10 years ago can still run fine today - and many still are. We reached a point in computing where upgrading doesn't make that big of a difference. You can use the same machine for a decade or more without problem if you're an end user, especially given so many rich web apps that don't require high processing power.
A Pentium 4 or Athlon XP 2700+ from 10 years ago has been unusable for all but the simplest tasks for years. It would have also needed to be upgraded along the way - it came from the factory with just 256MB or 512MB RAM. You can still edit office documents and do some light web-surfing, but for todays interactive sites and content it falls far behind the experience that an iPad can provide.
In an office environment, she really doesn't need more.