In an article posted by The Hollywood Reporter, Bruno Heller talks about the changes Selina Kyle went through in the season finale of “Gotham”, explaining that the character is still evolving:

Another character who underwent an unexpected change in the finale was Selina Kyle (Camren Bicondova), who went from street thief to gun-toting mole upon Fish’s reappearance. Heller explains that that doesn’t mean she’s turned evil exactly — more that she’s just a regular teenager. “Selina is one of those interesting ‘Gotham’ characters in that she’s ambiguous,” he says. “It’s still very much a story of a girl, not a woman, and teenagers try on different roles. She’s still a protean human being. We’re playing with that — she’s not going to become one thing or the other definitively until she’s a grown up.”

And if you wonder why we didn’t see Selina after she fled the scene whyle Oswald returned to confront Fish Mooney, here is the answer:

Fans might be wondering what happened to Butch or Selina after Oswald’s victory; Heller reveals that some moments in the finale were sacrificed for the greater good. “This world is so packed with incident and characters, it’s difficult to tell the story you want in the time frame you have,” says Heller. “There’s an element of an overstuffed suitcase with all of these episodes, because there’s so much to get in. You have to think of that as a virtue rather than a vice, because it’s better than vamping because you don’t have enough story to play with.”

As for the Batcave that briefly appeared in the finale, Bruno Heller prefers to call it “Bruce’s father’s office”, and reveals that it will play a big part in the next season:

Something that did make it in was that final scene of Bruce Wayne (David Mazouz) discovering a hidden passageway in Wayne Manor. Is that… the Bat-Cave? Heller laughs when the question is asked. “It’s a fireplace that moves sideways and goes downstairs,” says Heller. “It’s not the Bat-Cave, because the Bat-Cave only comes into existence when Bruce Wayne decides to become Batman. Call it his father’s office.”

What is in that office, and what it means to Bruce, will form much of the first part of the show’s second season. (“It’s very much a visualization of one’s parents’ secret lives, their past, when you’re a kid that age,” says Heller. “When you’re so young, the idea that your father and mother had hopes and dreams and secrets of their own. That’s what that staircase leads to. Dark secrets.”)