What would cause my 18yr old daughter to tell terrible lies and become vulgar and violent? She has told such detailed, extensive huge lies and has become so vulgar and down right mean towards me and very short tempered towards anyone and has even become v

Changes in behavior. Sudden changes in behavior of an 18-year-old could be drug and alcohol abuse or onset of a serious mental illness. Please take your daughter to a psychotherapist or psychologist as soon as you can get an appointment. Tell the doc background info on the phone, then let her go in by herself first so she doesn't feel you are talking about her. Therapists are skilled at getting teens to talk.
I . I am so sorry that this is happening to you. She may have an underlying psychiatric issue, and should be evaluated for this, although she may not agree to go. When people like, there are a variety of reasons. It can be to get attention or to cover up insecurities. Then when they know someone knows the truth about them, they get upset. She is taking out the anger at you. If she is violent again, you are going to have to call for help, as this could hurt you. Hopefully she will mature and realize that what she is doing is wrong and that her anger is misplaced. I wish the best for you.