I am totally out of the loop, so forgive me if this post is off in left field, but I wanted to weigh in on non-speakers of a language dreaming in that language.
I am almost on the cusp of being a B1 level French student, I am not a B1 yet. My ability to actually speak French is very poor as I am surrounded day and night by total Anglophones. My ability to free write is very poor and very painstaking with a dictionary open at all times and a conjugation tool open at all times, I am not able to write poetry at all in French. So there.
I sometimes dream in French, beautiful French I might add, but I am unable to actualize and realize that either during my lessons or with the few Francophones I deal with. I am very confident my French is much worse than CP Mary's Danish.
So my point is this, CP Mary may really dream in Danish on occasion.