Other mistake: When Claire Spencer loses her husband's mistress' braid in the lake, she tells him this and Dr. Norman Spencer acts like it's the first time he's heard her talk about it as he picks it out of the water. She has, however, mentioned the braid a short time before this to him, right after the rough sex they've had.
Other mistake: When Claire turns the hot water valve with the chain, it's turned in the wrong direction. It was turned to open it more.
Answer: There's no rule about how a step-father is referred to. Caitlin may simply not consider him a father figure to remain close to her real dad. Many step-children call their step-parent by their first name, regardless of how long the parents have been married. Most likely this is a plot device so that the audience isn't confused about or doesn't forget that Norman is not Caitlin's real father. Some may be offended by a father killing his biological child's mother. It makes Norman less attached to either Claire or Caitlin.
raywest ★
I am not trying to be rude, but have you seen this movie? You say that Caitlin might be close to her real dad. He is dead. Claire was "touring with a baby" after he died, and then she met Norman. Hence why I found the situation a bit odd. Norman has been in Caitlin's life since she was a "baby."
Azalea
I saw the movie some years ago and don't remember every small detail. However, my main point was that calling Norman by his first name was a plot device to keep the audience focused on him not being Caitlin's biological father. This kept his character more detached from Claire and Caitlin, and made him less sympathetic. It showed an emotional/personal divide existed between Norman and Claire and her daughter. He has less resistance in killing Claire if they did not share a biological child.
raywest ★