There are many hardware rewiews available from many sources both on the internet, and in magazines. They're even here at CNet. You did mention budget machines, so I assume that price is a limiting factor.

With that in mind, some things to consider:

Take her to a store to look at systems, with special attention to Monitors first. A "bad" monitor can give people headaches, see what SHE'S comfortable with.

Show her a trackball mouse, to see if she prefers that to a regular mouse.

Try out the feel of different keyboards, they may look the same, but ergonomically they aren't all the same.

Name brand packages come take it or leave it, and can dissappoint in some features. But they can be, to some degree, tailored to her needs. They also are likely to be highly proprietary internally, which usually limits your upgrade options. But, they all have a rather large pool of technical help to draw on if you need to.

Check out some of the surplus sites for "new" (unused) systems that are no longer cutting edge, just be sure to check that they come with warranty, and include an operating system.

An a-la-carte system usually winds up being pricier, but can be more satisfying. You can set it up for upgradability and comfort. However, you're on your on for support. So, if that's a concern, go with a brand name.

Since I work for a "brand name" company, I must recuse myself from making any specific recommendations.