Everything you need to know about the NCLEX is pretty much here: NCLEX - Wikipedia, the free encyclopedia
That being said there are two obvious answers to your query: either the person does not have the necessary educational background to answer enough questions correctly to "pass", or she/he is not seriously applying herself or himself to the situation.
Your friend should have received a Candidate Performance Report (CPR) from NCLEX after each failed exam. The CPR details her or his performance on the exam and includes how to use such information to better pass the exam next time.
Ideally your friend should be using the CPR to analyze her or his performance on the exams including areas that require more work. If after retaking the NCLEX five times and there is little or no improvement in areas noted on the CPR, even with all the claimed extensive review/study work, then something is seriously wrong.
The intent of the NCLEX is to measure if a graduate nurse is able to practice safely. If the answers as submitted to the computer tell this person is not likely able to do so, then they will fail.
I would suggest your friend gather up her five NCLEX CPR reports and seek out professional assistance. If her former program has post graduate counseling then start there, or find a coach or sympathetic RN who is able to sit her/him down and sort out what is going on.