Ok this may sound weird, but bare with me I've bean playing 40K since the 80's, this stems back to some Ye'oldie Minies I've got buried up back of my parents garage.
In the modern game are their Female Space Marines? way back in the day I got a Blister marked "Female Marine W/Plasma Gun" and an other marked "Battle Sisters" all had female characters (you can tell by the "Girl Bits" on the upper body molds and a couple of the heads) in power armor that otherwise matches Marine power armor minies of the time. over the years I've used them as Female Marines, Inquisitors, Sisters of Battle and general character models for IG and Imperial Agents in tabletop games.
I ask because one of my DH players is a Feminist, but wants to try DW and I may want to have the option of allowing her a Female character, also We've got an Antares Fan Boy who thinks he knows everything about Space Marines and I'd like to blow his mind with some "Lost Lore" from before he started playing 40K back in the mid to late 90's. back cica Y2K he chucked a hissy fit when I pulled out the Battle Sisters to fill out some squads when he insisted on a WISIWG game of 40K, they where Citadel/GW minies and the gear on the sheet matched what was on the Minies.
I've got the fluff worked out if it's allowable, Minor chapter with a stable verance in some lines of the Geanseed that allows implantation in to females, Stable Female Geenseed is rare and valuable, it is used to honor the heroic allies of the chapter by making their daughters in to Sisters of the Chapter.
If not it's no biggie Dudes can't be Sisters of Battle, so I don't see why the Antares can't be a boys only club