The best thing to do is to have a scary movie watching thing ( i recommend the grudge, ring, etc) then have one of your friends leve to do something, and not come back. Later on, after the movies, go to bed, and mabye make a little noise upstairs, struggle noises, you know. Then, the fun begins. Call on home phone, cell phone, you know, and make noises. My personal favorite is the grudge croak, but anything will do (breathing, jarbled whispers) and try to set the mood. Then later on have everyone come in the room and act really weird, and act creepy, and then all do the same noise you made on the phone at the same time, really scare her, then laugh, and have a good time. I dont know, thats what i would do, lol.

Watch the japanese version of The Ring at night.

Call her on her cellphone at 2am.

put like some dead thing in a room then have you in a costume as a killer or something

if you have a cell phone try to call her and sound different and if you have a costume put it on and when you think she’s freaked out about the scary phone calls sneak up to her in the costume and scare her make look like a horror movie but as scary as you can make it

tell her you cheated on her lol

Get her on scare tactic if the show is still running