Yeah, even the forum of the CICO site I use for tracking always stresses eating at least 100-200 kcal ABOVE BMR all the time. I don’t follow it (I have no idea about my BMR anyway, how could I? I have some vague guess but that’s it) but for losing I need to eat below my energy need, not my BMR.
And Ivy isn’t sedentary, has no much to lose either so eating so little makes no sense to me either. Very short term may be okay, even 0 calories are fine for very short term (I actually find fasting better than just undereating but only for a few days at most. she possibly has not enough fat for that so I wouldn’t do that either unless I would feel my body is very very fine with it).
Ivy, don’t stress over fat adaptation. It will come in several weeks, just do keto. I don’t know ways to get it super fast and what is long in the usual 6-8 weeks? It’s so little time in a human’s life… Things like this needs some time.