That’s just trolling, dude; given the price range, you won’t be able to find even a refurb anywhere close. While a Mac wouldn’t be a bad option for her, it’s silly to even bring it up in this conversation. And this is coming from a Mac user.
However, it does bring to mind another option outside of the range of nice NetBook/crappy Laptop – an iPad. I’ve seen refurbs and sales at places drop down to spitting distance of your $400 pricepoint; it might be worth looking into. I don’t say that because I think that an iPad is, in any way, a “full computer” (I don’t own one myself, because it doesn’t fit my needs), but it sounds like she’s a textbook case of the “target audience” of the platform – a lightly browsing, YouTube-watching, e-mail-sending user. These are the few things that an iPad is optimized for, user-experience-wise, and it means pretty much no tech support.
If you don’t like that idea, or can’t make it fit in the budget, I’ve had good experiences with MSI, Asus, and HP (EDIT: forgot Dell, those are great too) netbooks, personally. If she’s not a computer person (and therefore doesn’t “prefer” Windows), I’d even argue that you should install Ubuntu on it so that viruses aren’t an issue, but you may not want to/be up for doing that.
PS: Before I get flamed, I don’t mean this as an attack on Windows; Windows 7 (which came out after I switched to Mac) is an OS I’ve had great experiences with, and I personally run a VM constantly that is virus-free. However, newbie “parents” (and other users with limited knowledge, who end up coming to you when something goes wrong) are generally better off with a system optimized to not let them screw it up. The iPad is a great turnkey solution; a decently configured Ubuntu install is another such platform. I’ve had too many nightmares with friends & family clicking “allow” on something they shouldn’t have, and you just don’t have as many opportunities to bone yourself over on these other platforms.
TL;DR version – Yaaaaaay let’s all not have a flamewar yaaaaay.