They're Christian Young Adult novels. If not appropriate for a 14 year old, I don't know who they're appropriate for.

My advice is to not subject your friend to such bad writing. An extended family member recommended it to me, I borrowed the first book not realizing it was a YA series, got maybe 50 pages in and started wondering how someone's high school literature project got published. I googled it, which confirmed it wasn't worth the time.