Scream of Fear (1961)

Penny Applebee's parents were divorced when she was quite young and she grew up with her mother. After her mother's death, the wheelchair-bound Penny has accepted her father's invitation to live with him. She arrives only to learn that her father is away though her stepmother - who she is meeting for the first time - proves to be quite welcoming. On her first night however, she sees a light in the summerhouse and upon investigation, sees her father sitting there, apparently dead. Others can find nothing there and tell her she must have imagined it. She later sees his body in library and then again in the pool. She comes to believe that her stepmother and her father's friend, Doctor Pierre Gerard, are plotting to drive her insane. She gets a sympathetic ear from Bob, the chauffeur, who feels there has to be some rational explanation for what has been happening.