I've had a look through your previous questions bl08791 and I'm guessing this is about your younger sister. She has been through some traumatic times for anyone, let alone a kid.
There is possibly some insecurity there, I'm not qualified to make a judgement.
I know lots of people of all ages that do not like total darkness, some leave a light on in the house and their bedroom door open a bit so as not to be in total darkness.
I wouldn't be concerned about her having a dim light on whilst sleeping.
Insisting on removing the light completely could possibly create other issues.
Just continue being supportive.