There's hardly any fluff or anything really talking about the Sisters of Battle clashing with the Space Marines outside of "fuck it". Besides the only reason the SoB were there was because the IG were suspected of heresy due to the warpstorm.
and Dark Eldar were only there to rape, drink rum and collect souls and yet they were duking it out with 9 other factions for system domination like it was the good ol' days but it happened and it's canon unfortunately
As much as I would love being a female character (because I am, and I like to play a character based on me). Canonically I know it wouldn't be right, and I do care a bit more about the lore. I could settle with a Sister of Battle, or playing a faction that had women.
Yannow I've had some thoughts on this... can Slaanesh marines use theirs? Because if they can, then I have every reason to think they worked before turning to chaos.
Actually they have and will, it's a case if there's a major disagreement over something, or either party, or both parties, suspect each other of heresy. It is completely realistic and canonical to have the Astartes fighting the Sisters or the Imperial Guard fighting Astartes. Also, is anyone else annoyed by how people constantly call Astartes 'space marines', despite that they are properly referred to as Astartes and call each other such?