Re: 2.0, with additions
The thing with Sin remains an annoying nonsensical plot to me to this day, simply for meta reasons - the entire purpose of saddling her with the kid was to have an excuse to take her off the team as demanded by Editorial, but the whole purpose of taking her off the team was to put her on a different one, so an excuse that has her giving up heroism period is just utterly nonsensical and self-defeating - but it wasn't egregiously out of character for her. Dinah having this moment of impulsive empathy for a kid who has no one but her, and doing something really stupid like adopting her despite being a walking child endangerment case, strikes me as totally within the realm of possibility. If Bruce can do that shit three times in a row, I think the rather more empathetic Dinah's allowed one. Her then manning up and actually taking responsibility for that moment of stupidity and changing her life to accommodate it (unlike, say, Bruce) also seems well within her characterization (as is being literal-minded enough about family that she doesn't realize it's a less responsible decision than staying with the Birds). So: dumb plot arc, but not OOC.
As for Diana, she was obviously never going to get pregnant, so there's half the teeth out of that to begin with. And yes, that she would pursue it in this way and for this reason is.... "irritation" is a fairly mild word, actually. But that's not a reflection on Dinah. And it's still a sensual massage compared to the hot-coal-and-thumbtack bath of Miller or Kreisberg.