To overcome her posttraumatic stress disorder, a withdrawn orphaned girl, who suffers from hallucinations, decides to confide in a stranger and move to him being unaware he hides a horrifying secret connected with her past.

What motivates her to overcome her PTSD at this point in time? Or, in other words, what is her inciting incident?

Also, "...a horrifying secret..." is too vague a description for a logline - be specific, what is it about this guy that puts the girl at risk?

Lastly, as Craig said, what is her goal? Revenge against the guy? To overcome her PTSD? To find a family?

There is a difference between someone deciding to do something and someone doing something

In your logline she 'decides to confide in a stranger', however it would be better to say, 'she confides in a stranger'.

The character intro is a little long, it reads like a shopping list and doesn't inform story. ?What does she want to achieve? We need to see that. I think the wording around "move" is confusing. ?Here is an attempt but I don't know her goal.

"Hoping to get well a girl suffering to from PTSD and hallucinations moves in with a man, but discovering his past triggers a ....."

or

"the police don't ?believes a girl with PTSD and hallucinations but her carers murderous past forcing her to carry out her own justice".

You have a good character but I can't see a story. ?The motivation, character arc etc are for the script. ?This is the quickest explanation of the story.