Dreamerboy, I don't know how old your Mom may be, or what her mental state is like, but this whole thread reminds of my wife's mother, who is now 94, but who has exhibited some symptoms of senility for the last decade, or even a bit more.
We no longer are able to share certain kinds of information with her. If we tell her we spent $250 to get her dryer repaired, she will share that with any stranger she meets. At a recent funeral, my wife was embarrassed to hear her mother telling distant family members information about my wife' income: how much she makes an hour and so forth. She has been telling others that my wife's sister is "wealthy" (she's not; she and her husband farm, and just because soybeans are bringing $14/bushel, you have to realize that seed, fertilizer, fuel, and many other overhead expenses have to be factored in, leaving them with little actual profit). She no longer displays any measure of tact or sense of appropriateness in her conversations.
It's as if certain mental "filters" no longer function. Very sad, but it seems to be a function of aging.
So, I agree with many others in this thread. If you don't want her spreading information about your health, you simply cannot share that information with her. Even if she swears she will not spread this information, she assuredly will. And, it's possible that the onset of senility might be the culprit.