That means she was probably last seen or heard from that afternoon a few hours before the sub launched.
Edit: Here: http://ekstrabladet.dk/112/kim-isabel-forsvundet-i-ubaadsdra...
Also, the eyewitness accounts of the sinking make it sound like the sinking was deliberate:
"Kristian Isbak, who had responded to the Navy's call to help locate the ship on Friday, told The Associated Press he first spotted Madsen standing wearing his trademark military fatigues in the submarine's tower while it was still afloat. "He then climbed down inside the submarine and there was then some kind of air flow coming up and the submarine started to sink," Isbak said. "(He) came up again and stayed in the tower until water came into it" before swimming to a nearby boat as the submarine sank, he added." [3]
[1] https://www.reuters.com/article/us-denmark-submarine-idUSKBN...
[2] https://news.ycombinator.com/item?id=15000076
[3] http://time.com/4898129/submarine-owner-detained-over-journa...