I don't believe that being a Lesbian is a new social construct
Oh really?  Why do you think that way?
I believe some women have been Lesbians for thousands of years, but only recently has it begun to become acceptable. Thus, women are able to be more open about their sexuality. 
Yes, that's true.  TI does seem that we're being more open to more sexualities these days
It also can be cultural. Even in 2018, there are still some cultures that still frown on homosexuality.