First of all, EDUCATE,EDUCATE,EDUCATE!!! She has to learn as much as she can about nutrition. She needs to know WHY shes not eating those bad foods. Its not just about eating something that says "lowfat". Learn the ingredients, and what it does to your body when you eat them (ie: gluclose levels,how your body uses energy,and so on). When you know all the nitty gritty details of what things are made of and how the clog and poison our bodies, it will make you want to avoid them!
I totally understand the snacking problem, I eat out of boredom. So I try to find anything that will keep my mind off it and keeping busy doing other things. Tell her to take up a hobby, maybe even a healthy one!(I have a huge yard to maintain)
And when anyone opposes me to being healthy, acting like im over board... I let them know exactly how there making me feel, right then! I tell them Im sorry they dont care enough about me to want me to be the healthiest person I can be. And that it makes me happy and I prefer to not drop dead at 40 from a heart attack and that I want to be attractive(as much as i can be,lol) and healthy looking in my life. And I just brush them off and walk away with a smile. Usually they feel bad and realize how hurtful their words can be.
Im absolutely not saying shes not handling her money right. But discipline is a good thing to have in all aspects of life. Her making goals of moving out and weightloss all need that same "IM WORTH IT,I DESERVE THIS"-attitude.
Another big thing that has helped me with snacking is that I have a daily food journal. its a small cute spiral notebook. Everyday I write my food and some of the nutritional data,my daily weight,how much water I drink,that kind of stuff. its one way to keep track of some numbers but MAINLY its to keep me from eating things I shouldnt. Cause if im looking at something bad about to eat it i think "Im NOT writing that in my book". Its like you have to own up to it. No sneaking around.
I personally wouldnt suggest a water fast, at least not right away. She will feel weak and miserable and despise fasting. She could maybe start juicing one or two meals a day and slowly work her way to fasting. Then maybe do The Master Cleanse when ready. I just completed 14 days of an Master-Cleanse and it was amazing.I gained willpower I never knew I had! Im back to juicing 2 meals a day.
Anyways, thats just my 2 cents. Hope all works out!