Disclaimer- I am far from an expert on Meyers Briggs personality types, and have come to my own conclusions based off some reading I've done on it and the knowledge of my character. The format for this analysis is from MBTI-Typing Fictional Characters.
The Performer: People-oriented and fun-loving, they make things more fun for others by their enjoyment. Living for the moment, they love new experiences. They dislike theory and impersonal analysis. Interested in serving others. Likely to be the center of attention in social situations. Well-developed common sense and practical ability.
Strongest Functions: Extroverted Sensing (immediate action for immediate results, follows exciting impulses) to influence their Introverted Feeling (preference for peace over conflict, laid back, action-driven rather than spoken love).
Weaker Functions: Extroverted Thinking (planning, scheduling, and doing what’s necessary to accomplish goals) and Introverted Intuiting (an internal vision for the future, cautious in what they do due to their awareness of potential problems).
Extroverted: Claire loves sparing off both physically and verbally with her foes. She gets a lot of excitement and energy from interacting to others, and can get very bored and frustrated by herself, as evidenced by her complaining about the lack of vampiric activity she experiences at times. She like to assert herself to others and often acts without thinking.
Sensor: Her life motto is practically, "Act first, think later." She lives entirely in the moment and is highly impulsive. This proves to come very handy when in the middle of a fight and when needing to make quick decisions, but also leads to Claire getting in way over her head a lot. This is best demonstrated by her accepting her duty as a slayer without really stopping to consider how this will effect her relationships, schoolwork, and future. Yet even when her impulsive nature lands her into trouble, she can always rely on it to help her get out of it.
Feeler: Claire is very sensitive to how others view her. Being patronized for who she is causes her to want to show off and prove others wrong. She relies on her emotions to make decisions rather than reason, and often ends up landing herself in trouble because of it. Though she tries to convince herself otherwise, she is very wounded by the fact that her friends and boyfriend left her when she started to act strange and the disappointment her parents have in her thanks to her behavior. The frustration she has over Joanna comes from not being able to receive emotional comfort from her when she needs it.
Perceiver: Claire can easily adapt to whatever environment she's in and use it to her advantage. She's a very fun-loving and witty girl, and can lead to her bringing a lot of light to rather dark situations. She loves the adventures and thrills being a slayer brings to her life and gets bored when it comes to a stop or when she has to come back to mundane life.