I don't recall her ever saying in an interview that she was not heterosexual. I do remember Beanie and Ben Platt talking about their friendship and going to their high school prom together.
I suspect that she was never closeted. She just didn't go around shouting it to the world. At some point, perhaps after seeing Booksmart, I must have checked the Wikipedia article that said she identified as queer, a term I (personally) don't feel comfortable in using, given that it had such a disparaging connotation when I was growing up.