"War of Principalities...."

Hi! I'm asking someone with a good working knowledge of the Bible, to tell me where that piece of Scripture is located that has the words, "it is a war of principalities...". I'm a Christian, but not very educated. Also, discernment has not been my strong suit. I want to find this verse and study it. A friend of mine is a really good person...as in kind, good deed doer, loves to learn new things, and is open to all of life's many experiences. She has had some experiences, while checking out "haunted houses" and ghosts and things like that, and these experiences concern me. She has had a dark feeling of oppression and I worry that her sweet, young spirit may be under attack by demonic forces. As I am a "young" Christian, I don't feel smart enough to explain to her why maybe she should lay off the ghost stuff. God Bless All and help us to help each other. Peace. Hyiath