Are there any official stats and rules for sisters of battle in dw? I was thinking they might make a good force to secund into the deathwatch as auxiliary troops that are far superior to most guardsmen, far more loyal and devout than inquisitor henchmen and highly effective while still being cheaper than space marines. Sure they're not as powerful or durable as Marines but are, in cold terms, cheaper and easier to replace too. Add in power armor and bolters plus access to special gear from the ninistoirum and they could be an attractive option to the deathwatch. Hell, give them access to some dw gear plus bionics and they can come close to a stock marine in power.
They could be assigned by the ecclisarchy or possibly 'recruited' because they saw something that they should not have seen but are too loyal and devout (not to mention valuable) to just put down so they are given the chance to serve the emperor as deathwatch forces.
Also in game terms they give an excuse to have female PCs for female players. The only other way I can see a female pc in deathwatch would be a female inquisitor and I don't know if dw has rules to make an inquisitor.
If there's a new edition of dw I hope it adds some options for female PCs and sisters of battle are a God possibility for that.