If you want to tell her, it may help, especially if she has BP, she may already guess...
You will act like yourself... And, depending on the person, the Dx can be helpful, not just by itself --- you may have to educate people you want to know (if you were a diabetic, you might hide it, but it would be easier to explain why you need to turn down certain foods, and disappear several times a day to check your glucose---and what they can look for should you have symptoms of hypo/hyperglycemia, could save your life----) I don't see MI as any different when handled as a matter of fact. There are some good resources on this site that you could send to anyone you wanted to communicate with---lots of people think they know what you mean when you speak the name of a diagnosis, but many really do Not know what you mean unless you educate them....Best to you!