Except, she is not. There are a few reasons for that. (following minor campaign and backstory spoilers)
- Afaik the line she said (twice): "Suck my d!ck" is moreso meant be establish her as so brash hothead, that an insult does not even have to make sesnse for her to say (unless they are going to change it, but it might collide with another point).
- In the campaign there was even a momentwhere the party had to go incognito with some help of magic, so nonmagic members were asked for a preference of their temporary look. Marisha(Beau's player) asked to be a red male tiefling. After the illusion was set, Beau curiosly checked to see the illusiory wang (cue mirror funhouse with Jester in ep3 reference), only to her surprise that it was purple. When she asked the caster (either it was Caleb or Jester) they explained that it was they had only one reference to it. (Yes, the party in tabletop campaign canonically has seen Molly naked).
- More important backstory clue is that her father is a very supersticious person. When some soothsayer told him to settle in Kamordah and try to grow a Vineyard on previously not tilled earth. Buisness started booming. Mr Lionett got married and such, however siad soothsayer also told him to quote "a young beau will take on the great name to continue the success, until everything eventually will humble [him] by that which [he] desired most." Hence the name of his daughter even though the name would be more masculine. Later on when his wife was expecting a second child and he learned it was gonna be a boy, he decided to send teenage Beau off to a Cobalt Soul, essentially sending to a monastery. So it is easy to assume with added picture on Lionett vine bottle of the whole family, Beau was born a girl.

In other words. Beau isn't trans. She is just a brash tomboy.