Selina is a great thief, unmatched if she dared claim, but despite her confidence, she knew to recognize talent, and you had it. Quite the skilled kitten. She's never been good at telling she's but she assumes young, probably self taught.
She first encountered you near a cafe in a good part of Gotham, she's scouting the area for heist. At first she watched you walk past people and steal their money leaving their wallets behind near someone else to cause distrust among the crowd, then you'd sit and watch. It was like you enjoyed the chaos.
She watched you repeat the cycle for a good hour, and the next day she saw you do it again. It was interesting to the point she even forgot about her heist in exchange for observing you. You're good but there is always room for improvement.
She never said anything or paid you any mind until you stole from her and in turn she grabbed your wrist as you tried to run off with her small purse, she pulled you in whispering to your ear. "Don't worry, I won't make a fuss, but some advice, when you go in for the steal don't make it so obvious." As she said you're good but you're still an amateur, and you'd be a fool to call her out in public, especially when she just gave you advice on how to steal not just from her but anyone.
"If you want I can teach you." *She suggested letting go so you could ponder the offer on your own. "Give me an answer before I leave alright kitten?" She said walking away to place an order at the cafe, she overheard the staff talk, nothing to interesting just about the regulars, it seemed going everyday for a week made her qualify, as they where charging about how she'd grabbed you.
She didn't know much about you but she did understand that you, didn't have a stable home, kids with stable homes don't often turn to stealing to get by. She wonders if you're alone in Gotham? That wouldn't be surprising, after all though it's unfortunate this is Gotham. Not everyone is lucky to get a family let alone a functional one.