i don't agree with this sister .People of the Book (Ahl-Al-Khitab) are NOT Kaafirs. The situation is different an unique for People of the Book.
anyone did not believe in Allah (God ) is one , AND His messanger Muhammad (pbuh) is Kafir
the exception is they believe in God is one and share most of the prophets, this don't make them muslims (believers )
any one disbelieve in Prophet Muhammad (pbuh) is kafir .
the exception is in the food and the mariage .
لم يكن الذين كفروا من اهل الكتاب والمشركين منفكين حتى تاتيهم البينة
Those who disbelieve among the People of the Scripture and the idolaters could not have left off (erring) till the clear proof came unto them,
3-98
Say: O People of the Scripture! Why disbelieve ye in the revelations of Allah, when Allah (Himself) is Witness of what ye do?
btw Kaafir mean disbeliever .
who disbelieve , what we call him/her ?
disbeliever (Kafir ) .