The problem does indeed seem to be with the Gale database, which seems to support sharing to all kinds of places, but not Diigo. We can't access the article from the bookmark. If the girls highlighted healthy sections, then that's pretty good, but if they were planning to go back to the article, not so good.
It's tempting to just say we'll use the web, which I know will work, but our school is paying for this very nice resource with things that are not necessarily out there in internetland. A bit of a disappointment.