My 2 step children are identical to this little snot. But at least they have the excuse of being adopted out of foster care. The boy is 16 and his sister ( same mom different dads) is a pathological liar and a thief and his 11 year old sister is the same except she shows signs and is being treated for Narcissistic Personality Disorder, Bipolarism, & Schizophrenia but at her age won’t diagnose her.
They regularly see behavioral psychologists every week and a shrink once a month since they were each 8 years old. They have no sense of right or wrong, empathy for anyone or anything, and cannot distinguish between reward and punishment.
As for this girl leaving home at 18, I’ve told the boy that I will wake him up at 12:01 AM on his 18th birthday and show him the door. Even his professional medical folk agree and told us they would do the same thing!
You best be up that whole night then.