Hiya, first-time d&der, got a human now cleric who tried to follow in her father's(paladin) footsteps to defeat drow king with evil undead army, instead gets taken prisoner and tortured for 20 days until her party rescues her. Torture includes light,-sleep deprivation and emotional abuse, with cat-of-nine-tails scarring on back. Besides the easier to research symptoms of PTSD, any advice to flesh out a backstory?
My advice for fleshing out a backstory is to look beyond just the trauma.
Trauma survivors are fully fleshed-out humans beyond our traumatic experiences, and your character’s history and existing self-perception will have an impact on how she responds to the trauma. Have a look at the Traumatized Character Profile - if you look at the “things that complicate trauma responses” section, you will see that things like your character’s pre-existing coping skills and previous history of trauma (which includes things like previous experiences of battle, or childhood abuse) will impact on the severity of post-traumatic symptoms.
Look into the support structures she has, and what experiences she had prior to the torture that might shape her responses. What was her self-esteem like before this?
I would advise exploring her relationships with family and friends back home - how close were those relationships previously, and how would these loved ones react to her in her traumatised state? Worries about their reactions and her own feelings of failure will complicate her response, and if she has a negative reaction when she returns this is likely to be harmful to her recovery.
If you want to find out more about the effects of torture check out @scripttorture who has lots of information, including this list of the common effects of torture.