Blue is for Nightmares -- Laurie Faria Stolarz
Judging from this book, Laurie Faria Stolarz may well be the Lois Duncan of this decade. (The writing itself wasn't so hot, but that isn't really an issue. The book was such a page-turner that it was over before I had a chance to groan much.)
Blue is for Nightmares had it all: romance, suspense, terror, magic:
Stacey Brown, latest in a long line of Wiccans, has been having nightmares about her boarding school roommate. This is the second time that she's had a recurring nightmare about someone close to her--the first time, she did nothing and a little girl died. This time, she is determined to prevent the murder--and she isn't afraid to call on the forces of nature to help her. Cue spooky music.
It isn't necessarily a book that I'd buy for myself, but if you need something to recommend to a semi-reluctant reader who likes magic AND romance-y realistic fiction AND horror movies, etc., etc., this might do the trick. (Although I probably wouldn't but it--well, not for full price--if the library gets the other books in the series, I'll totally read 'em.)
(After writing all that, I double-checked: Lois Duncan is actually still writing. I read a ton of her books when I was in elementary/middle school, so I'll always think of her as a 70s/80s writer.)