what happened to the nurse ??

If you're talking about the nurse who went to the basement to fix the telephone/computer servers, I'm pretty sure Dr. Ryan found her in the basement by the smashed up computer, right before "the boogeyman" electrocutes her. I forget how he kills the nurse though.

she was killed by the Boogeyman

are you going to bark all day little doggie,, or are you going to bite

When you see the other nurse saying the boogeyman exists before Laura tapes her mouth up, You can see the other lady behind her on the floor.

She was killed off screen by the Boogeyman in the same manner the mother was in the beginning of the film (stabbed through the throat).