The recent Worlds' Finest Annual featured the young Helena Wayne as Robin battling some crooks and taking one out in a particularly nasty manner:
That's an iron poker right through the chest and stomach, killing the guy. Self defence could be argued, sure, but she still kills him.
Later on she, Supergirl and Wonder Woman battle Fury who had previously killed someone that Supergirl was sweet on. Fury gets away through a Boom Tube, leaving Robin to report back:
"She's a killer."
Yes, Robin, she is. Just like you.