Good Intentions But....Eh...
I just need to get right down to the nitty gritty on this one and say I'm struggling with this one. The premise by which Helena begins her journey into superherodom feels a little bland. Many, many superheroes have lost a parent (or parents or paternal figures) they loved dearly and use their own personal angst to begin a crusade against the world's injustices. It's fair enough incentive but when it's compared to Helena Bertinelli's origin, of which most of us will inevitably refer to, this one pales in comparison.
Yes, Bertinelli lost her parents and brother but the context had so many more layers seeing as how she wasn't fond of her father (and actually openly expressed her wishes he'd die mere moments before) and ended up being a darker, grittier, and (most importantly) less predictable character. Also, there's something of a characterization issue with Bruce being opposed to Selina taking out Helena for a patrol seeing as how he's let his much younger, much more unstable son Damian out with him in mainstream continuity.
Power Girl or Supergirl rather, is an interesting element and oddly fits her new incarnation a bit more snugly but the bonding that occurs between herself and Helena just moments after Selina dies is somewhat...inappropriate. It all felt pretty lukewarm to me.