There are female Custodes, which are bespoke mutant super soldiers made with the same fundamental tech as space marines, except tailored to the individual instead of being mass produced from goopy bits salvaged from the necks of dead space marines.

Space marines are jobbers and suck, anyways. They basically exist to show up, do the dumbest thing possible, suffer >60% casualties to establish threat, and then one designated protagonist with plot armor carries the day before also dying in a big heroic sacrifice - through this, they accounted for .01% or less of their side's forces and killed maybe .02% of the enemy's forces at best. They are the most deeply unserious faction in an already silly setting that struggles with having numbers make any kind of sense at all, and at their best they're just a football player sized guy in heavy armor who runs in with reckless disregard for his own safety because he does not understand what "death" is and who shoots pretty good because he's spent a long time practicing shooting at things.