As I recall, this diet was developed by a doctor as a means for athletes to lose weight and retain lean muscle during the off season. It would seem to me that it is counterproductive to enter into a high intensity training program, such as preparation for a 10K while on Phase 1.
I know people who have regained the weight as well. As with anything, if we learn nothing while on IP we are bound to return to old/bad habits. It is very important to phase off of P1 properly to begin restarting your metabolism and pancreas. It is also very important to increase your protein consumption if you are exercising.
Many of those who have regained will tell you that they did not phase off properly and went right back to old ways of eating. Her comments would give me even more incentive to stick with it.
Don't look back, you're not going that way!