It doesn't matter what you consider the norm.
It matters what GOD says.
It also doesn't matter whether she sees it as religion or if it's just trendy, it's roots are that of evil and no, you absolutely shouldn't keep them just because you believe she innocently gave them to you as a gift.

I find it very hard to believe that anyone would buy crystals without having a basic understanding of what they are. It's pretty common knowledge. Which is why I say she probably knew what she was doing. And... if she's such a good friend, she'd know your beliefs, right? At most, I assume she knows you're christian. That alone should have been enough for her to know better.