First of all, does your friend do ANY physical activities??
If not, then you'll have a lot more on your plate.
Motivating some one to get and STAY active takes patience and a will from your friend, since its going to be rather tough for her at first. Make sure there is lots of encouragement and a clear goal is she is to remain on this plan.
Start off with small exercises if she doesn't do anything now. A balance between cardio and weight-lifting always gives the best results. Start off with two-pound weights, and do curls. Keep her elbow in the same spot at her side and lift up towards your face, and down about 60-70 degrees. Do AT LEAST 30-40 repetitions. I have always believed this is the most basic and first step to weight-training, and while it sounds easy, for someone who has no muscle definition, you'll feel the burn after the first 20 repetitions. You may do these in sets of 15.
For cardio, depending on your friend's level of fitness, can start either easy: walking for half an hour straight with no breaks, or medium: a light jog for 20 minutes with no stopping, and a 10 minute walk.
These are the first steps people like your friend can take in exercise. However, if your friend, like many people also do, does not curb her diet to fit that of what weight she WANTS to be, then exercise will do little to change her weight.
For her height, your friend should weight around 110-140 pounds. So, your friend's bmr is about 1800 calories at the moment, or how much she needs to eat in a day to keep her at her current weight.
I suggest she cuts out about 500 calories from that, meaning she should only eat 1300 calories in a day.
That is a big jump from what she may be eating, but you can start with small changes, like cutting out any sodas will really help with the first few pounds. (A helpful little thing to know is this: your stomach is supposed to be the size of one of your fist. Servings for meals should be about the size of your palm. That's when you should stop.)
After your friend gradually fixes her diet, and builds up her resistance through exercise, you may begin to really notice improvements.
Remember to always stay motivated and never give up!