If the answer is simply that you believe another OS will support more (though maybe not all) of her hardware, why not at least recommend that she get a Live CD, try it and see? Then she can weigh for herself the benefits of a (mostly) Free software OS against the extra cost of getting her hardware to work, instead of just accepting your guess that it's not worth it.
Sorry, this is an unreasonable expectation, and one that should be corrected, not reinforced. The "average user" has no right to expect that an operating system should work with any and all hardware, simply because one operating system has a monopoly position with respect to users and a monopsony-ish position with respect to hardware makers. It hurts all computer users, and Free software users in particular, when we allow such companies to set our expectations.