There is a little more info on Eva Schloss in this interview with Markus Lanz on German television (ZDF) from October 2014. My German is not good, but I gather that in this version, she and her mother were not selected for the gas chamber by Mengele. However, her mother was selected later on and then miraculously survived, though only after Eva had told family members that she had been gassed. Her father and brother though, were selected for the gas chamber by Mengele, but also miraculously survived. They were sent to Mauthausen and apparently died at some point later.
(No surprise incidentally, that the New Statesman has deleted all comments on the linked article, hence illustrating our opponents customary confidence in the success of their arguments in an open debate.)
It's nothing new, since you got the same type of testimony at the Frankfurt Auschwitz Trial (selected to be gassed, but then not gassed anyway), but at least we got it on video now.