It's suggestive of the early stags of Operation London Bridge getting underway and the private doctor briefing family, Government and selected media outlets. Wouldn't surprise me if there is big news over the Easter Bank Holiday
That's not how London Bridge would work - lots of people know about its workings (military, newsrooms etc because they are incioved in aspects of the planning and the regular reviews) and it begins only on death, and and announcement is made promptly, there is very little time for family only, as all the formal phone calls politician here and in to dependent territories need to be done, and newsrooms alerted with the embargo time - its an hour or so?
That's the time when you might notice pre-changes - as broadcasters will start to chose more subdued playlists - no one wants the 'we break into the programme ...' announcement to be in the middle of Mr Blobby
But they really won't be keeping her on ice.
If she was seriously ill in a life threatening way, then I think the Palace would confirm illness. As they haven't, there may be a growing list of issues, which might be normal ageing or medical condition, but which are not any immediate threat