Most men, at one point or another, have been caught in the friend zone. There are specific reasons and behaviors that get men caught in this trap.
Men get caught in the friend zone when they fail to make an appropriate "move" on the girl that they are interested in. Other factors that are responsible for getting you caught in the friend zone include:
Playing therapist as she complains about her ex-boyfriend.
Going shopping with her.
Trying to solve all of her life's problems.
Don't get me wrong, these behaviors are perfectly okay if you want to be her friend or are already her boyfriend. But these are not going to help you attract her in a romantic way. Remember, she has girlfriends for this stuff.
What you need to do, is step away from the situation entirely. If you have hobbies, get back to them. If you don't, find some. Just start to develop a high quality life and just spend less time with this particular girl. Go out and meet new people. Focus on your career. Just be less available to her and give her the gift of missing you. When she calls or texts you asking where you have been, just tell her that you are busy.
Once you have learned how to create a great and abundant life, this girl will now see you in a whole new light. She will have noticed the sudden change in you and hopefully she will now want to be more than just friends.