I'm guessing she's speaks in a chic or hip manner in Japanese and this is how the translator adapt it in English cause there's no direct equivalent.
I appreciate your thoughtful reply. I'm sure that's the logic, but it reflects a stunted sensibility on the translator's part for how the translated product actually reads to the target (English-reading) audience - "aight" simply isn't chic for this character, it's cringe. If the affected manner of speaking even matters (I don't believe it does, but if so), then something like "Kay" would actually sound like something a school girl might say - among many other choices that might have been better in this context, I'm sure. There might not be a "chic" way of merely saying "All right" in English - in which case, it would be a mistake to force it.