Hi Sally,
Here's a link to a study that demonstrated that in rats, at least, this type of silicon supplement was quite bioavailable and helped prevent femoral bone loss:
http://www.springerlink.com/content/w4l84266q80m320x/A tip for getting this kind of information is to find the active ingredient in any supplement about which you're curious, and to type that into the Google Scholar search engine, removing the engine's ability to provide patents along with the studies.
However, silicon is but one ingredient for healthy bones. She'll want to be sure her vitamin D3 levels are optimal (50-80 ng/mL), that her digestion is supported if necessary, and that she's got a full complement of all the other necessary nutrients. You might want to consider a whole foods bone supplements, such as Right Foods "Daily Bone Care." There are studies indicating that minerals, at least, are better absorbed from food sources.
Is she checking her urine pH? That's kind of fun (if you're a nutrition geek, I guess), and it would enable her to track at least one aspect of her progress.
And exercise, I believe, is key. My 82 y.o. mother has osteoporosis from many years of corticosteroid use for what was finally diagnosed as Crohn's disease long after she stopped using them. She walks, dances, does yoga and aerobics -- she's kind of unstoppable. She eats well (E4H, basically, with some sweets everyday) and supplements mainly with whole foods supplements. She took a couple of nasty falls within the last two years, onto hard surfaces, and didn't break a thing. This is, of course, different than a woman who is already experiencing fractures, but she can only start from where she is.
One last point, Fosamax, Boniva, etc. ARE indicated for
severe osteoporosis. That's an unpleasant consideration but they DO add substance to weak bones. Since many people die of pneumonia while "recovering" from fractured hips and such, they may not be such a bad option if her osteoporosis is bad enough. In general, though, while they promote density, they do not increase strength, so her decision to see you is a brilliant one.
Good luck.