Well it sounds like your friend had a similar reaction I had, I mean a friend of mine had, where I, I mean she, was able to enjoy a special occasion one day and be right back to normal fat burning the next day. Early on with Keto, this wasn’t the case and I, she, was knocked off course for a good 3 days minimum. Then later with several months of adaptation came the ability to go “off plan” and get right back on the next day. What doesn’t work - I can tell you for sure, is to go off plan for several months. That will result in your friend needing to re-start all over again.