Good questionning. Yet, I wish to point out that if she is exaggerating a physical illness that she may have a mental illness instead.

How close are you to this individual. Are they a Facebook acquaintance or someone close to you in real life. I ask because personally for me there is a big difference between the two. If it is the former I would be inclined to shrug it off as not my business. However, were this to be person you also know apart from social media I would gently indicate I am troubled by the whole matter. I would approach it from a standpoint of letting her know you are concerned. "That seems like a great deal of caffeine to me. It causes me to worry about you a little." It need not be an intervention. The discussion could even go like, "I didn't realise coffee was good for cardiac patients. Is this a new idea?"