My older sister used to also be extremely selfless in our family, she´d always help others and put herself last. She was also very reliable.

When she moved out of our parents´ house something began to change. She started to lie a LOT about all kinds of things, even when there was no need, in my opinion, or when it was obvious that she was lying.
She did it mostly I think, to get her way, get out of uncomfortable situations or just simply didn´t have to do things she didn´t want to.
Sometimes, it seemed really, for no reason at all.

Examples were, she would take for example some of my Cds or clothing without asking or telling me and when I asked her about it she would lie and tell me she didn´t take them. When I would see my Cds (or other things) at her place, she would lie further and tell me that her roommate had the exact same Cds as me (when it was just obvious that it wasn´t true).
I thought it was weird, because I knew it and she knew it and she knew that I knew it. This might seem normal for like a 13 year old to steal from her 16 year old sister or something, but she was 21 at the time and past that stage, I´d think. Besides, it didn´t really match her personality to do something like that.

Friends of her once said that she had become a very frequent liar, too. So it wasn´t just with me.

Then she started to cancel appointments with me at the last minute again and again and make up excuses that were obviously not true. I don´t know but I felt like this was a "power" thing.

Basically, I feel like she went from being a "very good girl" to someone who would treat others disrespectfully for no apparent reason "secretively".

I wonder if this is common to happen when someone needed to be a "too good kid" in a family with not enough attention for herself, then moves out and then sort of goes into the other extreme when out of the family environment, maybe simply because now she "can".

Has anyone heard of this before??