Well, we know she was supposed to be 16 just before Infinite Crisis since Dr. Light made some rude comment about how the League had reduced his brain to that of a 16 year old girl and Cassandra, Raven and Mia (Speedy) all took offense to that.
So considering we had the OYL barrier following Infinite Crisis, she did likely end up at being 17 or maybe 18 by the time Flashpoint hit.
As much as I like demigoddess Cassie, I can't help but think the demigod origin took importance from this scene
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"You can't be everywhere, you can't do it all"
"I'm not Batman, I have friends."
"But listen, call yourself Bat-Chick, Knightbat, or Black Robin- the point is, don't forget- you have a family."
"You don't need me. This is a job for.........Alfred!" -Tim Drake
"Dear Diary, I know what my next science project is going to be called: "My love/hate relationship with Gravity........And it was only then that young Stephanie truly realized gravity would forever be her enemy. "-Stephanie Brown
Cassie in Bombshells United #1
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And Cassie hugging Donna IMG_9771.jpg
And that's not all
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So since this is Bombshells... who wants to guess how long it takes before Cassandra and Donna show a little more than friendly interest in each other?