It could get even worse for Brianna if she does decide to admit her trans status. Besides shattering her most sacred lie, there's years of material out there where Brianna has talked down to women "as a fellow woman", spoken from the perspective of a biological woman on sensitive subjects like reproduction, gotten speaking events and panel positions she wouldn't have been involved with if she were a man, and so on. While there's a segment of the far left that might not have a problem with any of that (at least not openly), most women have a very real problem with someone who isn't even biologically a woman trying to insinuate they are more knowledgeable or a better representative for them on subjects like women's health.
Basically, I don't see even a short-term gain for Brianna if she came out now; she's put too much stock into the image and it's clear that she benefited by hiding her status potentially over actual, better qualified women.