(I'm posting this publicly because I had no other means to contact the writer of the message and if I didn't post it soon, I'd COMPLETELY forget about it)
I enjoyed reading your character premise and certainly think it's plausible and can lead to a very dynamic individual. What makes characters stick in people's minds, imho, is not WHAT they do but WHY.
I'm a student of comic writer Chuck Dixon's school of thought in that I believe you should answer 3 questions about your character & once you do, the stories begin to write themselves. Those questions are:
What do you like about your character? - what qualities does she have that make her admirable
What do you NOT like about your character? - what qualities does she have that make her reprehensible
What does your character WANT? - this is the hardest question to answer but once you do, everything else falls into place
To use what you've described about your character for example :
She not only works with children but she helps them even when committing crimes, an admirable trait. She doesn't want children to suffer.
She kills people however, so she doesn't believe that justice can be achieved through society's normal means. She also doesn't accept her own responsibility for her actions as, say, a vigilante who would leave a calling card of some kind.
And the main key is what does she WANT? Does she want to stop child abuse? Does she want to envelope abusers in the same fear their victims feel? Does she want to continue to do this anonymously, using her actions to represent something bigger than one person's crusade against abusers?
If you take any of the above and go into greater detail, you create all the plausibility you need to create an interesting character. I hope to read more about this person who is out to punish abusers & I'm especially looking forward to learning just what it is that she wants. I hope this was helpful and not overbearing