I have a new friend who asks me if a person is able to help the police with an investigation by some kind of knowledge that will help save a person's life, can that be evil? She argues that it saves people's lives. She says it's dreams or some kind of ESP she does that saves lifes and she believes it's a good thing and of God. I believe it is some kind of demonic influence and a form of acting as a medium. What do you say?

You didn't really state what your friend does, but I'm guessing that she pretends to help the police by offering "psychic" readings regarding crimes. As you suspect, God is quite clear that these sorts of things are wrong. "There shall not be found among you anyone who makes his son or his daughter pass through the fire, or one who practices witchcraft, or a soothsayer, or one who interprets omens, or a sorcerer, or one who conjures spells, or a medium, or a spiritist, or one who calls up the dead. For all who do these things are an abomination to the LORD, and because of these abominations the LORD your God drives them out from before you" (Deuteronomy 18:10-12).

Your friend is justifying what she wants to do, despite God's statements on the matter, by saying that if good results, then it can't be wrong. In other words, she is saying that the ends justifies the means. Paul stated, "And why not say, "Let us do evil that good may come"? --as we are slanderously reported and as some affirm that we say. Their condemnation is just" (Romans 3:8). Evil remains evil regardless of the outcome.

A secondary problem is that your friend is not being honest. She might have had a few lucky guesses, but she is not completely accurate (the truth is that psychics are rarely correct). Thus in hopes of giving a lucky guess (because these thing originate in her own mind) she costs the police many hours of fruitless labor checking out worthless information because they can't afford not to check out everything presented to them.

See also:

Questions and Answers regarding Psychics
Keys to Understanding: Reasoning Without Truth