Don't go on a diet for a long time, it's very tiring, and after it is reduced to a certain extent, the body will adapt to the state of less intake, so it won't have much effect, and it is easy to rebound and be depressed if you eat more than before.
Can be interrupted. For example, eat Robb for three days (three days and a week are free according to your own situation and perseverance); Drink yogurt; Drink honey water; Vegetable soup; Porridge and so on. (These methods I mentioned are based on them) If you persist, you will gradually return to a normal diet. It is best to have a process from liquid diet to semi-liquid diet and then to normal, which is better for your health and your body has an adaptation process, so it will not rebound. You can spend two days a week, such as Sunday and weekend. Of course, you have perseverance and determination, and you can persist for a week. I have a friend who stayed at home for a day in the summer vacation and fell asleep (reducing consumption). He woke up to drink porridge, a bowl of clear porridge. He lost 10 kg in half a month, and lost more than 20 kg in a holiday. We didn't recognize him.
Reminder: Everything should go with the flow, just try your best. Don't be too extreme. Good health is the most important thing. Don't suffer from stomach problems, especially bulimia nervosa or anorexia. Wish your sister success. Happy new year!