Is this a hero of time thing? I figure she’s talking about time loops, and Dave did seem pretty chill about the alternative Daves…But then Dave is chill about everything. Maybe it’s a result of her having to sacrifice all the Aradiabots to beat the black king. Aradia basically had to orchestrate a mass suicide of her selves, so she probably already dealt with the moral issues there. 

Or maybe it’s because she was killed when she was like what, 10 or 11? And lived for years as a ghost afterward. That’s got to skew your perception of life and death.