Has your friend Helen ever had to lose a substantial amount of weight? And what will you do if you find you aren't "drifting down"?
I'm not saying what she suggests won't work--just that sometimes things look simple "on paper" and turn out not to be satisfactory in real life.
Also, I'm a little confused about what she's suggesting. What does it mean to "eat what you need to eat to 'Maintain' your weight in the future"? If that means no special foods, no really heavy restrictions... well, that's what calorie counting is anyway.
I assume you still need to have a target number of calories for the day... That's what "diet" means for me: Calorie restriction... In my own experience, exercise alone, without watching food intake, doesn't work.
Well, if you want to try what she suggests, why not? You'll know within a couple of months whether it's working for you.