Stumbling through the Internet today, looking for something else, I came across a possible explanation for that behavior, as well as her seeming addiction to watching the set (or a computer monitor) and why she seems to often be a changed person after watching for a while.
…people who were watching TV …reported feeling relaxed and passive. The EEG studies similarly show less mental stimulation, as measured by alpha brain-wave production, during viewing than during reading.
What is more surprising is that the sense of relaxation ends when the set is turned off, but the feelings of passivity and lowered alertness continue. Survey participants commonly reflect that television has somehow absorbed or sucked out their energy, leaving them depleted. They say they have more difficulty concentrating after viewing than before. In contrast, they rarely indicate such difficulty after reading. After playing sports or engaging in hobbies, people report improvements in mood. After watching TV, people's moods are about the same or worse than before.
Within moments of sitting or lying down and pushing the "power" button, viewers report feeling more relaxed. Because the relaxation occurs quickly, people are conditioned to associate viewing with rest and lack of tension. The association is positively reinforced because viewers remain relaxed throughout viewing, and it is negatively reinforced via the stress and dysphoric rumination that occurs once the screen goes blank again.
Habit-forming drugs work in similar ways. A tranquilizer that leaves the body rapidly is much more likely to cause dependence than one that leaves the body slowly, precisely because the user is more aware that the drug's effects are wearing off. Similarly, viewers' vague learned sense that they will feel less relaxed if they stop viewing may be a significant factor in not turning the set off. Viewing begets more viewing.
My daughter is a TV addict, are you?
However, I must admit that an occasional mental massage by the TV does feel good.