What does this even mean? Do void creatures sexually reproduce? Some do but others don't? Do they have another purpose to this dichotomy other than reproduction?
Or is it just Riot going "Look we can make a female character that isn't tits and ass, lols!"
Based on pieces of lore it would seem she is part of a "species" of Void creature currently native to the Shuriman desert. She is the largest and most powerful, and so it is possible she is their "mother".
My guess is that Void creatures do not technically reproduce. All share a theme of collection, be it physical matter 
, traits 
, worshipers 
, or knowledge 
. Due to her nature I would say Rek'Sai, with her territorial nature, is designed to take over land. A singular creature would be able to control a large area, however the Void always want's more. That is where the smaller members of her "species" come in.
I believe she either has some way to asexually reproduce, or can somehow generate lesser Void creatures. The only way I can see anyone figuring it out in lore would be to see if these smaller creatures grow into what Rek'Sai is, or if they stay weaker. The community does not know what the facts are on this, however I'd bet money it has something to do with whatever her Void ancestry wishes her to collect.
The only other time lesser Void creatures are mentioned is when they enter through a portal, so either Rek'Sai is protecting a Void portal (in which case why is there only one type of creature coming through?) or there is some form of reproduction or creation going on.
TLDR: The community has wanted a female monster character for a long time before her release, so it's possible Riot started making her just to show they can do it and to appease the community. That said the finished product is far more than Riot saying "Look we can make a female character that isn't tits and ass, lols!".
Well, Chogath. Velkoz, and Kogmaw are all confirmed males. I thought it was interesting that they chose to make Reksai female. I mean, they could have made the character male, but they chose not to.
It means they created a female void creature.
That's it. They don't need a reason or justification on it.
I was thinking it kind of relates to ant colonies and bee colonies and things like that where there's a queen.
