I do wonder if it is possible for her to avoid this operation.

Yes, it is always possible. Keep in mind that bone is constantly being broken down and rebuilt is a process called remodeling. So the bone can be rebuilt if given what it needs. Again silica is the primary bone nutrient that declines with aging. Cartilage can also regrow despite what the doctors say. I have seen it done plenty of times.

She's off the Atkins thankfully.

re: the spring water. I drink that, and find that when I boil it -i drink a lot of boiled water, often plain- it always has a lot of calcium (?) I assume, that collects in the bottom, as well as a thin skim of something. Do you feel that the minerals in spring water are really bioavailable, given their size? I have wondered about this, of late.

Boiling the water concentrates the minerals as water is lost through evaporation. The concentrated minerals are precipitating out, which is why you see the minerals on the bottom. Not sure what the skim is, this should not be from the water. 

Yes the minerals are absorbed. Think about it this way. In all the time humans have existed on this Earth we have drunk mineralized water from lakes, rivers, wells, etc. and we have always received benefits from these minerals. The minerals will react with stomach acid converting in to readily absorbed salts. In addition acids formed by the intestinal flora also convert minerals in to absorbable salts.

Do you know anyone who's had this operation? Or managed to reverse the damge that would suggest needing it?

I know people who have had the operation and have done pretty good with it. But the replacements are not permanent. They generally need replacement again after about a decade.  And there was some big problem with some of the implants a while back that was being reported but I do not recall all the details. Something about early failures due to poor manufacturing if I recall right. But I have also seen numerous people reverse bone damage and regrow their cartilage.  The body has the ability to heal if given what it requires. But healing ability does decrease with age, but again this is primarily due to declining stomach acid levels, which decreases the absorption of nutrients.