Frist things first, her "friends" are pieces of shit for not supporting her and subhumans for mocking her, she should start by losing them before the flabby tummy.
I agree with most of the things said here but I'll add my two cents anyway.
-Refined sugar is the devil and should be avoided like the plague, that includes soft drinks and juices. Designate a day a week where you can eat a sweet (ice cream, chocolate, cookies). Once you go trough the withdrawal symptoms you are good to go.
-No alcohol, alcohol and sugar go hand in hand and have the same effects on the liver.
-Intermittent fasting, look up Dr. Fung.
-Diet breaks. Long story short, diet at deficit for 2/3 weeks and go back at maintenance for 2/1 weeks, repeat for 5/3
months and go back at maintenance for a month. This helps prevent plateaus and the slowing down of the metabolism.
-Keep an active life style even if you don't enjoy exercising. Go out for a walk, find a friend to play some sports with, find an hobby that isn't just binge watching tv or YouTube for hours on end
-Be severe but not harsh with yourself, learn to love and listen to your body, take your time because you're in for the long run. Remember that everyone is different, you need to experiment and find out what works well for you.
-DON'T GIVE MILK TO CATS this one has nothing to do with dieting but people should know.