Don’t keep junk food in the house. No cakes, crackers, pretzels, chips, ice cream, candy bars etc. If it’s not there she can’t eat it.
Make sure she has protein for breakfast. It can be a protein shake, egg, or plain Greek yogurt (I add a little honey to mine)
Make a fruit smoothie but load it up with spinach too (my daughter and I drink one daily). They are very filling.
Don’t eat after dinner. If she wants something, have a cup of tea.
Go for a walk every night after dinner.
Take a dance class, martial arts class, yoga class or whatever floats her boat.
Fyi... My cousin lost over 100 lbs through weight watchers. She said being accountable to someone (ie. knowing she would be weighed weekly) motivated her to lose the weight. She said she also didn’t know how to eat healthy until WW taught her. She told me she really didn’t have a concept of portion sizes.
Tell her this is 12 week plan. After 12 weeks I’m betting she will be so happy with the results she’ll want to keep it up and by then she will have new habits.
Good luck!