Does this sound like a pathological liar?

Okay i met this girl 9 months ago, and I became friends with her. At first she seemed like such a sweet person but later on she turned out to be completely different. She was always lying. Even about stupid things that didn't even matter. I liked a guy on her street, and she lied and told me that he likes her, and that her cousin is married to his brother and they have 2 kids. She also made a fake facebook and hotmail account with his name and pretended to be him. My friends and I didn't believe that that really was him because i had only seen him, not met him, and her parents didn't even allow her to talk to him because he was much older than her, and she was always talking about how they are so close and that she goes to his house and talks to him. When we told her we think she's lying she got all defensive, and she made a fake facebook conversation where she tells him what we thought, and he gets angry. She's been carrying on this lie for 8 months now, and I finally figured out she's lying because the person who i talked to, who was supposed to be him used the exact same language as her, and she has a dirty mind, and he used to talk about sex in almost every conversation. My friend is also her cousin, so i asked her if the cousin who "Supposedly" married his brother is actually married and she said no. She's alo told SOOOOO many other lies but there are too many for me to write about. If anyone doesn't believe what she says, she always gets all serious and defensive. Nobody likes her because nobody trusts her. I think something must be wrong with her, but I'm not sure.