Paranormal Activity 2

August, 2006, a "burglary" occurs at the home of Kristi (Sprague Grayden) and Daniel Rey (Brian Boland). The entire house is trashed except for their infant son Hunter's bedroom. Dan installs security cameras throughout the house after the vandalism, which capture many strange occurrences. Martine (Vivis Cortez), the Hispanic family housekeeper and nanny, goes into Hunter's room after hearing a loud bang and senses a demonic presence in his room. She takes him downstairs and attempts to cleanse the house of "evil spirits" but when Dan arrives home and catches her burning sage, Martine is fired.
Kristi believes that their home is haunted and tells Daniel. Daniel reviews the footage but dismisses her claims. Kristi talks to her sister Katie (Katie Featherston) about being tormented by a demon when they were little girls. Dan's daughter, Ali (Molly Ephraim), begins investigating the mysterious occurrences, and discovers that humans can make deals with demons for wealth or power by forfeiting the soul of their first-born son. She also discovers that Hunter was the first male to be born on Kristi's side since the 1930s.
The violence quickly escalates; The family's German shepherd, Abby, becomes aware of the demon's presence and is attacked. Dan and Ali take Abby to the veterinarian, leaving Kristi alone with Hunter. When Kristi checks on the baby, the demon assaults her and drags her down to the basement, where she stays for an hour. Finally, the basement door opens and a possessed Kristi walks out. The following day, Ali is home with Kristi, who will not get out of bed. She finds the basement door covered in scratches and the word meus (Latin for "Mine"), etched into it.
Ali goes upstairs to check on Hunter and sees Kristi there, with a strange bite mark on her leg. When Ali tries to get Hunter, Kristi furiously orders her not to touch him. Now terrified, Ali begs Daniel to come home. After he arrives, she shows him the footage of Kristi's attack. He immediately calls Martine, who prepares a cross to exorcise the demon; and tells them that Kristi will have no memory of being possessed. Since the curse can only be transferred to a blood relative, Dan tells Ali he is going to pass the demon onto Katie, so that Kristi and Hunter will be safe. Ali begs him not to because it is unfair to Katie, but Dan sees no other way to save his wife and son.
That night, when Dan tries to use the cross on Kristi, she attacks him, and all the houselights go out. Using the handheld camera's night vision he finds that Kristi and Hunter have disappeared. Furniture starts to topple over, and the chandeliers begin to shake. Dan chases Kristi into the basement, where she attacks him. After he touches her with the cross she collapses. Dan hears demonic growls and finally, the shaking stops. Dan puts Kristi to bed and burns a photo of a young Katie (the same photo Micah later finds in the attic of his and Katie's house in the first film).
Three weeks later, Katie visits and explains that strange things have started happening at her house. She then returns home to her boyfriend Micah (Micah Sloat). On October 9, the night after Micah is killed, a possessed Katie breaks into Dan and Kristi's home and kills Dan by snapping his neck while he watches TV. She then kills Kristi in Hunter's room, violently hurling her at the camera, and takes the baby. She leaves, cradling Hunter, and the screen fades to black as Hunter's crying turns into laughter.
An epilogue text states that Ali was on a school trip, and she found the bodies of Daniel and Kristi upon her return home and that Katie and Hunter's whereabouts remain unknown.

Question: Who is upstairs with a strange bite mark on her leg?
Answer: Kristi