In Gothika, why does Rachel Parsons torture the innocent patient Miranda instead of her rapist, Sheriff Ryan?
Apparently she cannot affect her rapists in any way, but Miranda is prone to her influence.
Upon her escape she fled to the river bridge and plunged herself to its depths. Her angry spirit however continues to haunt the only person that can see her ghost, Doug's wife, Miranda.
The ghost of the boy that Miranda sees at the end seems to confirm that she has a "gift".