Their input and opinion can change her orientation then can cause her to be unhappy with herself annd give her the mindset that she should change for the people around her.
Her friend's opinion will change her own opinion about herself, and not only will that make her self-conscious, but also it will impact her self-concept.
To lose body fat a very good strategy among the ones which you've listed here would be to create a calorie deficit - c. When we have a caloric deficit, the calories can start to burn from the energy stores found in our body which are also known as fat cells.