In thinking about the question, I thought, "Well, you could politely ask the person how they prefer to be addressed."
But then I thought, "That might offend the person being asked." I guess it depends on the person.
As for me, it would be no problem, this late in the game it's like water off a ducks back.
I was standing in the check-out line and this little old lady tells (I guessed) her granddaughter, "Go stand in line behind him."
I wasn't sure who she was talking about. Then the little girl came and stood behind me. I chuckled to myself and said to the lady,
"It is HER." She turned red and said, "Oh, I am so sorry, I wasn't paying attention.
I saw the camoflage pants and hat and assumed you were a man." I told her, "Don't worry about it, I get that sometimes."
Like water off a ducks back. I wasn't offended but I wasn't going to let it slide either.
Just in case there was anyone within earshot, having any question as to how I prefer to be addressed.