Been enjoying the Adepta centric stories, but they don't bother to list any chronological order on Black Library, so what do you folks suggest ?
There isn't really one
Warhammer 40k is not a single series - instead, it contains lots of unrelated books written by different authors. There are of course some small series following one certain group of characters i.e. "Gaunt's Ghosts" which follows one Imperial Guard regiment or various "Omnibus" books (Ultramarines/Iron Warriors/Blood Angels/whatever) or books that focus on certain important events like the "Horus Heresy". But in general, the books are unrelated and often even contradictory - for example, the primarch Alpharius has been killed in at least three different books (yet he might still be alive) or the same Space Marine Chapter Master being at the same time killed by Eldars and alive fighting Tyranids.
Looking at the official Black Library page I've found about 50 (some of the titles repeat itself with different translations, some might be false-positive) books marked as "An Adepta Sororitas novel" and, from the look of them, only 3 are part of a series ("Broken Saints" trilogy"), the rest seems unrelated to each other. So just take your pick and keep reading in Emperor's name!
There Isn't Really One (Mostly)
Most of the Sororitas novels and stories are completely self-contained and standalone.
The one exception to the rule are the two novels Faith & Fire and Hammer & Anvil and the audio drama Red & Black.
These all deal with the same cast of characters with Red & Black being a prequel to the first two that involves the same characters but with the events that transpire not really being relevant to the two novels.
Faith & Fire leads into Hammer & Anvil and sets up a lot of references and callbacks. It's not 100% necessary to read Faith & Fire first but you'll miss out on a lot of significant characterization and emotional investment for Hammer & Anvil if you don't read it first.
In summary, the stories for all three stand alone just fine but if you read/listen out of order you'll miss out on a lot of backstory and character details.