Why does she do this?

My younger sister has anorexia and aside from not eating that much, she also has these really strange habits and rituals that she's been doing ever since she was diagnosed.
-She goes to bed at 8pm and wakes up at 5am everyday.
-She doesn't do her laundry sometimes. She'll wear the same clothes a bunch of times before my parents tell her to wash them because she begins to smell.
-She purposefully leaves the water running when she brushes her teeth and will get very upset if you ask her to shut it off.
-She measures food with measuring cups and spoons and will get very angry if you ask her why she does it and even had a panic attack after my mom hid them in an attempt to break her out of it.
-She eats peanut butter sandwiches (the only nutritional food she really eats) but she cuts the corners of the bread off.
...Just to name a few.
Any reason why she does these things?

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