Windmills, I'm English - and know the term well - Hi there!
Ex had black-outs a lot, and it wasn't strictly a case of waking up and not knowing what he had done the night before (although that also happened): I've seen him switch out of a black out, where he appeared to have most of his cognitive faculties intact (but was obviously drunk), but just lost all filed memories of that previous timeframe, like a wiped computor memory.
I've also seen him slip out of one straight into another, where he had no recollection of what he did/said in the preceeding half hour but could remember before that and what he had just said, and then 20 mins later he lost all recollection of the whole past hour: I won't say he was exactly mastermind at this point, but he was walking, talking, fairly lucid....
If the words and behaviour are unnaceptable, and she continues to make clear decisions that make those consequences (her words and behaviour) more likely - I think you have the answer you need, whether she really believes the stuff she says at that point or not is sort of irrelevant, if she has stuff she needs to get off her chest there are far less destructive ways of getting it out than drinking into a black-out......