Talking on Netflix's Afterglow roundtable discussion alongside actors Ella Purnell, Hailee Steinfeld, and Reed Lorenzo Shannon (Jinx, Vi, and Ekko respectively) showrunner Christian Linke says that the end of act 2 has set things up for an explosive final act.

I fell in love with Arcane at first viewing, but there was one thing about Silco and Jinx's relationship that has only just begun to make sense.

Isha is an orphan child from the Zaun undercity. After Jinx saves her from Chem-barons Chross and newbie Smeech, Isha starts following the blue-haired Zaunite around, looking up to her as an idol and mentor, hence the nickname “Baby Jinx.”