Answer: Emotional numbness
Step-by-step explanation:
Kathren is not having any emotions or expressions while watching a humorous episode on TV because she is dealing with emotional numbness.
She is feeling isolated, uconcentrated and she is clearly unable to think deeply so she doesn't find that episode funny until her mom points her to smile and then she is getting to notice the episode.
The cause of this kind of numbness is mostly anxiety and depression.