Do you think i am overreacting over my sister's behaviors?

I think my sister has gone mental. She's one year older than me. I went to same schools with her all my life, so I thought I knew her pretty well. However, she seems very distant and very....off nowadays.

My sister and I are very different. She's very extroverted and I am introverted. I understand the difference but these days she seems like she's not herself.

She steals stuff from her part time job - not money but things like chopsticks, food, and towels, etc. I have no idea why she does this when they are things that don't even cost much.

She seems very violent and impulsive. She says things like "I want to slap you so hard but I'm holding it back." and she doesn't put things where they were at supermarkets and leave them on the floor.

She also is very compulsive about a few behaviors. She barely cleans and her room is full of trash all of the time, but she screams at me when I sit on her bed without changing to my pajamas. She literally shouts at my face if I drop something on the floor as if her room is not full of hairs lying around.

Last week, my family was visiting where our school is at but she was busy drinking and going out with her friends. She barely showed any emotion or had conversations with them. She fixed her eyes on her cell phone screen talking to her friends and laughing at useless things.

I really wonder what has gotten into her. It's not that her going out and drinking and having relationships bother me. But she's doing things that are morally wrong but I wonder if I am overreacting?