4 teens get sucked into fantasy world, can’t control when they go back and forth, have to deal with a queen of death, cover had a half rotted face

[Grace]

I read this book 15ish years ago, so 2005. I know it was part of a series, it was ya and the main characters were teenagers but I found it very creepy. I don’t think the teens were friends before being in the fantasy world. I know the main characters were not from the world they were In, somehow they were sucked into the fantasy world and had to survive. I remember vividly them having to confront a antagonist who was some kind of queen of skulls and the dead. The cover had a face beautiful and have creepy and rotted face in my edition.