I believe it was due to a...trade? I allowed Venkman to borrow her for about a half an hour, and when he gave her back, she evolved...somehow. Though I don't see how that triggered such a dramatic change.

[Faraday seems to light up at the question as she taps on Egon's shoulder, gesturing towards his bag. He barely looks in her direction as he hands her a small notebook. She flips through it, then opens it to show Jolene her beautiful pencil drawings.]

But that's quite incredible. Kölliker can read rather proficiently, as well as Faraday. Though I don't believe I've actually facilitated the education of the creatures under my care.