Why does large pixel size matter? Do you really want all her images to look pixellated and all her text to have the jaggies? LCD pixel size depends on the physical measurements of the screen and the res to which you have set it. You set the screen res and/or screen font size so she can read comfortably, end of story. The smaller the picture unit (used to call 'em "triads" on CRT monitors), the smoother your text and images can look at any res. That's why CRT can still give smoother images than LCD at any res it's capable of displaying (they didn't really have defined pixels until the slot-mask models which introduced the word "jaggies" into the monitor lexicon) and it has always been the smaller the dot (triad) pitch the better. Generally, LCD only looks reasonably smooth at native res or perhaps at even fractions of it.
. I just got my first LCD and sometimes its images look really awful relative to the CRT I just closeted... Text has generally looked good.
. Perhaps "pixel pitch" is the term you were looking for. In any case, smaller is generally better. Picture units at lower res are just made up of more screen "pixel pitches".
.bh.
PS: Jeff, below, is basically saying what I'm saying here. You want a screen size that will display at least 1024x768 res (as most web pages are designed for it), but at a size it's easy for her to read. I found that 1024x768 was too small for me to read comfortably on my 17" CRT, so I generally ran it at 800x600. My new LCD is a 19", wide screen, and is just at the edge of comfort at 1024x768. But I'm probably a youngster (at only 61 y.o.) relative to your granny. OTOH, 60 can be great-granny territory in some locales... .bh.