Guillian-Barre is NOT caused by the flu shot. G-B is a condition that can attack the body after a virus has been contracted. Your friend is risking lives by refusing to get a shot. While she may not contract the flu, she can still be a carrier, and infect any patients she comes into contact with, many of whom may have weakened immune systems and will contract the flu and could possible die.
There are risks with any vaccination, but unless your doctor has directly advised you not to get one (as your doctor did), or you have an allergic reaction to one, you should still get them. Smallpox was at one time eradicated in our country due to vaccinations. Now, because of scaremongering and people refusing to get vaccinations, smallpox has cropped up again. People die from smallpox, they don't die from vaccines (except in very rare cases).
Influenza viruses go through what is called "drift" - the viruses change slightly in order to still be viable in the host, which is why there is a different strain of the flu each year that makes people sick, even if they had the previous year's strain. Scientists study the viruses every year to try and determine which ones have drifted enough to cause an outbreak - usually they get it right. As science is imperfect (as are humans), occasionally they miss a strain, and outbreaks are worse than usual. Usually the worst times for that are the years when a certain virus will go through a "shift", which means it changed enoug that almost no one will have any immunity to it, and almost everyone exposed to it will contract it. This was the case with H1N1 a few years ago, and the reason there was no outbreak is because the shift was caught by those scientists and they were able to develop the vaccine in time to stop it.
While formaldehyde is used in the manufacture of the vaccine, it is removed before the vaccine is packaged, so you don't get more than a trace amount, which can't hurt you.
Here is a link to the CDC's information about what is contained in the vaccine and how harmless it really is.
http://www.cdc.gov/vaccines/vac-gen/additives.htm