My belief only:
Well I don't think her gender plays any major role to the boys who kissed/liked her because technically she is biologically genderless, neither male or female. The only reason she considers herself female is because she was a female in the human world and that mentality carried over, so she considers herself a girl. But to the other people/entities/boys that live in that world, they know elemental people are without any biological gender, so they don't care much?
You do have a point that she's biologically genderless but some of the boys that kissed/liked her and some people that she meet so far don't know that she's an elementalist instead they think she's a summoner/sorcerer. which makes me more confused because after Haein was badly hurt and taken home by her father, the duke said something like "i won't let him go"...?(sorry,i don't remember what he said) then he clenches his fist. that makes me think that the duke is referring haein as a boy?
HEY HEY FELLOW SIMP
if Haein or the mc is sometimes mistaken for a boy does that mean all the dudes that kissed/liked her are gay or do they know that Haein is a girl?or she just looked like a girl?