Diet investment
She has invested a good sum of money in her diet already. She might not notice it but, she did and she continually does as she tries and tries new things. How many glasses and flavors of shake she has tried? How many crash diets with menus hard and expensive to prepare? I guess, she has not found the best diet pills yet. Yes, the one that will really work for her. I think those pills start with letters E and D.
Your guess is right!