You are chatting with [person A] about nothing in particular, when [person A] uses a male gendered title! But isn't [person A] totally a girl?! This bothers you! Oh my goodness, what should you do?
a) realising you are really not clued up on this situation, you quietly and politely ask [person A] what pronoun you should apply, without digging for juicy details.
b) [person A]'s gender may not be exactly as you thought! That sounds awkward and weird, though, so you pretend you heard nothing and continue to use female specific words only.
c) ha ha, silly [person A] has clearly forgotten that that title is a MAN title! You helpfully point out her mistake, she is a girl and should use girl words! What an airhead!
HINT: If you chose c), you are EXTREMELY FUCKING WRONG