Ok, let me offer some helpful advice to DC for bringing Cassandra Cain back into the New 52 fold. I've boiled the character down to 10 simple points, the bare bones elements for a recognizable Cass Cain re-boot.
1) Of multiracial heritage, born and bred to be the perfect assassin.
2) Raised with movement as her native language. As a result, she has a limited vocabulary of words in any spoken language (to be precise, she knows a handful of English words), but can communicate through gestures and posture.
3) This training gifted her with the ability to read her opponents' intentions before even they're fully aware of them. It has also made her perfectly empathetic in that she can read emotional states and even micro-expressions with an incredible degree of accuracy and understanding.
4) One of the finest (and deadliest) martial artists on the planet. Top five ranking, maybe as high as number two depending on who's "on" that day.
5) David Cain, her biological father, abused her horribly during her initial training. It could be said the training itself was abuse. Cass has a love-hate relationship with him.
6) Killed a man at Cain's behest as a child, the event left her guilt-ridden and even suicidal as she experienced the man's terror personally because of her intense empathetic state.
7) Wandered the earth while she attempted to deal with the emotional fall-out of having murdered.
8) Death wish.
10) Endlessly tenacious.
See how easy that is, DC people? And it would make so many people happy.
At the risk of complicating matters-- we could argue whether or not having Lady Shiva as her mother is essential as well. I lean towards pro-Shiva maternity. For one thing, change a parent, get a different person. Plus, if we accept one of the character themes here is "nature versus nurture," having a killer like Shiva provides even more of an obstacle for Cass to overcome and establish herself as one of the "good guys." Shiva's lineage might also supply some of the base talents on which Cain built his unstoppable engine of destruction. Having issues with both parents adds some thematic bookending as well, plus generational conflict-- A Jack Kirby-esque element which provides a call-back to one of DC's most storied eras and something that could be played up for dramatic effect.
But since we can also argue that no one in the New 52 is exactly the same person as in the previous DC universe, this aspect could be negotiable. Especially if changing it results in a stronger character (somehow) or a classic story. I'm willing to trade almost any aspect of continuity if in return I get a superlative reading experience.