This should be brought to risk management. The very nature of patient privacy is such that a social media page is in direct opposition to that.
Regardless, your friend stepped over a boundry when private messaging this patient. It is always good to remember no matter how charming and nice and funny a patient is, the ER is not a match.com meetup. And call me jaded (haha play on words there) but if a care nurse is private messaging the nice, cute funny...and all the other adjectives this patient was described as... the motivation was perhaps not "gee whiz how are you" stuff.
One nurse I know got fired after a person took a picture of her caring for a family member and posted it, and tagged it, and comments not very nice about the hospital were made by others who received the tagged photo. (and tagging pictures sends it to 500 friends and 500 friends friends and so on and so on). Nurse had no control over that, however, lost her job anyways. Still another who was in a managerial position and contacted a patient (after misread "signals"--whatever that means) and the patient flipped out and the nurse was no longer a manager. Patients have lives outside of the hospital, and as nurses we should as well. That doesn't include getting personal with patients. Even if your friend finds herself face to face with an irate sister, mother, girlfriend, fiance, wife or obsessed ex. What happens in the ER stays in the ER. Good lesson learned.
Gone are the days that people talk about patients in the hospital with the best of intentions, give them a little jingle to see how they are. Unless you are the follow up person after discharge, and then that is usually pretty scripted.
Remember your professional boundries, that they are patients and not friends (and sometimes friends are patients, but story for another thread).
Once any hospital administration realized the extent that a social media page can travel with tagging and posting and commenting they may have no choice but to shut it down. And I don't know about you, but I don't want anyone posting pictures that may include me--my work life is my work life, my personal life and social media my own.