So there might be some slight spoilers here proceed with caution.

So this is a bit of a random theory I have come up with but I think it's good. It was mentioned that Catwoman's secret could tear her and Bruce apart in the Designer story. At first I thought that maybe it was the whole money thing but now I think maybe there was more to it that has Catwoman scared the Designer came to Gotham around twenty years prior to that main story. We also know Punchline was a college student at least in her Sophmore year. So Punchline would have been conceived and born around the time of the Designer's death. Also the more I look at Punchline the more I think she's looks like a younger Selina with blue eyes just like Bruce. There's also the fact that Joker seems to like her but I think there's more to it. I think it's in her name I think she's his ultimate joke on Batman and I think Selina's secret that will tear her and Bruce apart has nothing to do with money.

I got to thinking about this when I got to the part where Punchline fought Harley and way she beat Harley reminded me of when Catwoman "killed" Joker, she slit Harley's throat and of course Harley when into the water. My point however is that it was similar to what Catwoman did to Joker. I can't help but wonder if it was on purpose to have a detail like that in there. So basically my theory is this Batman knocked up Selina, she didn't tell him and gave the kid up to give it a better chance but instead the kid lived a miserable life and Joker found her (but pretended to be found) and decided to mold her into his partner.

I mean it would be the ultimate way to screw with Batman if you think about it Joker taking Batman's own daughter and making her in his image would really screw with Batman's head, and Batman would likely never forgive Selina if she kept something so huge and personal from him. I just think it would make for a hell of a twist with Punchline's character if she really was Batman's daughter.