What if Chloe Bourgeois was Stephanie Brown's long lost sister?
I don’t feel entirely confident in my knowledge of either of their characterizations/histories, but here’s an attempt at something!
So, before they even meet, Chloe has some differences due to being adopted.
In some ways she’s worse with her actions in trying to hold her mother’s attention and jealousy of Zoe who is her mother’s actual biological kid. But in other ways she’s better, due to feeling less like she fated to hold her high status and more like she has to earn it through being “Good”
Steph finds out about the connection first, so is the one to reach out to Chloe. Not exactly when this’d best fall in the timelines, but it’s probably either pre-canon or early-canon for Miraculous Ladybug
Chloe… doesn’t know how to feel about this. On one hand, Steph represents an actual blood-familial connection she could lean into (something she’s lacking) that might not have the same “I need to be good enough to earn their care” stress, but on the other she’s still caught up in her own issues about being “good enough” for her mother and is hesitant to act away from her adopted family
But Steph is perceptive enough to notice Chloe’s insecurities and whatnot just from reading their letters. She relates to parts of them (after all, she’d been overconfident and gotten in over her head before, and she recognizes Chloe’s at times arrogant attitude as a sort of defense mechanism), so she pushes for them to keep in contact since she believes that they could become genuinely very close with time.
Thus, they continue sending some messages back and forth, and over time this helps contribute to Chloe further improving as a person.
These changes are actually enough that Ladybug agrees to let Chloe keep using the Bee Miraculous sometimes, though not without some definite stumbles in their interactions along the way
Also would probably have to remove the “Chloe publicly declares her hero identity in one of her plans” thing to work with this
Neither tells the other about their hero work though. Steph can tell that something is up that Chloe isn’t telling (i’m including the crossover trope of an “information block to prevent foreign heroes from rushing in unprepared and getting akumatized” thing), but doesn’t know what and is hesitant to try to pry
A bit further into their communication, they decide they’d like to meet in person at some point.
However, Chloe is nervous about bringing her to Paris because of the Hawkmoth situation, and she’d be unlikely to get permission to go the other way (I could see her mother in particular forbidding it as “a ridiculous diversion” unless she knew Steph knows Bruce Wayne and thus their interactions could have “business potential”), so it gets kinda put off.
But then, after [some notable akuma event, IDK which would be ideal], the idea of her leaving Paris for a bit for safety gets brought up, and she jumps at the chance to push for going to Gotham to meet her sibling.
Well maybe it’s more like she pushes her parents to go to l New York, but then convinces the people she’s staying with there to bring her to Gotham
Alongside talking to Steph, she has another goal with this: to talk to the Bats.
Yeah, she’s still worried about heroes coming into Paris and getting akumatized, but she hopes that as detectives the Bats could give assistance remotely. Specifically, searching for Hawkmoth’s identity and/or base of operations.
And maybe, if she’s lucky, they’ll help her train to be an even more capable hero when she returns to Paris…