Other mistake: When Ruby is signing onto America Online to check her mail you hear the dial-up sound before she even clicks on the sign on button.
Other mistake: In the scene where Ruby is writing her parent's lawyer an email, there are no cables connected to the computer she's using, and still she's able to get online. She can't be using an airport, because then you wouldn't get the dialling tone.
Other mistake: When Rhett sees Terry coming up from the car accident that he was in and tells Ruby, she jumps in the front seat of the car. The car is in park, but she moves the lever up, which would mean the car was in the drive position already.
Answer: My theory is that Terry deliberately acted like a creep to make Ruby uncomfortable around him. If she accused him of being inappropriate, he could deny it, making her look like the "troublemaker." She already has a history of being in trouble at school and sneaking to parties/raves. And he set her up for another accusation of plagiarism. He probably wanted to get rid of her because, unlike her brother, she was not fooled by him and Erin. He later points out that they only need one of the children in order to get the money.