Of course they did handwave that away with the whole Deathstroke magic evil juice stuff (and then never gave us any follow up on Cass dealing with killing people against her will - even in Beechan's mini when she's back wanting to murder Deathstroke and her father which further proves Beechan had no idea of the character at all - even when he had plenty of time and incentive to think about it).

Jason doesn't have that excuse (unless you want to say the Lazarus Pit damaged his mind - which it probably did).

It any good can come out of the reboot its that the Beechan-era Cass never existed anymore (heck I'd wager that Cass's whole career as Batgirl never existed anymore).