Okay I recently struggled with this same issue and I decided on nursing for a variety of reasons. The main reason for me, was patient care. The focus of nurses is patient care. Yes, ofcourse nurses use their medical knowledge to help patients, as do physicians. They differ in their jobs on the FOCUS. The main job of nurses is the PATIENT part of that sentence; the main job of physicians is the MEDICAL part of that sentence.
Again, ultimately both jobs use medical knowledge to help patients...but the focus is vastly different.
I think your friend needs to decide what aspect of care she wants to focus on. Is she doing this job mainly for a love of science? For an interest in the human body? Then I think your friend should become a doctor. Is your friend doing this mainly because of patient care? Then I think your friend should become a nurse.
Other then this, there are many other things to consider as well. First of, how much time does your friend have? Becoming a doctor is 4 years of undergrad+4 years of medical school + a minimum of 3 years of residency. Becoming a nurse is a minimum of 1 year of prereq's + 2 years of nursing school (as the shortest route, if your friend goes straight to BSN then it is 4-5 years).
Also, what kind of money does your friend need to make to support a lifestyle? Doctors make more money then nurses. A lot more. Nursing makes enough for me to support my lifestyle, but it may not for some people.
How much debt is your friend willing to go in? If your friend plans on becoming a doctor, your friend will have a lot of debt. They will probably make enough money to pay it off, but it will take awhile.
How important is authority to your friend? I'm not saying that nurses don't have authority, but in general they tend ot have less then doctors. This may or may not be important ot your friend.
How important is it to your friend to be able to "switch"? What i mean is, as a doctor if you become a pediatrician it is difficult to switch to oncology (fellowship, and still you will probably have to work with kids). If you are a pediatric nurse and want to work with adults, it is just a matter of getting hired in a place working with adults (which isn't necessarily easy once you have started working somewhere to switch, but its easier then it would be for physicians).
How important is a flexible schedule to your friend? In general it seems that nurses have more flexible hours, in terms of 12 hour shifts 3 days a week instead of having to go in everyday. Also, when a nurse leaves work, generally speaking the nurse is off duty. This isn't necessarily the case for physicians, many carry beepers, etc (not true of all physicians again, I am speaking generally).
All in all, those are the main points I would urge your friend to consider. If ur friend is still having difficulty deciding, he/she can always get a BSN and use the elective credits to complete the premed requirements. At that point, if your friend decides to become a doctor he/she can take the mcat and apply. If he/she wants to do nursing then they can forget that and study for the NCLEX.
Just a thought.