Soundtrack Suggestions

Some names of some sounds in GarageBand i think that are suitable and could possibly use are:
Borealis
Most of the sounds that are under the "Textures" category, especially Mystery Accents 04
Modern Rock Guitar 12 and 13 also stand out
Rock Guitar Riff 01 and 02

I think that during the parts where the girl is picking up the letter and walking upstairs should just be sound effects and have either very quiet and subtle music or no music at all. The music should come in whenever we have any activity with the intruder, building the suspense and making it more suspicious. It would also make it clear which parts are of the intruder and which is of the girl.

In the very end scene the music should slowly build as the intruder is opening the door and perhaps then have a dramatic spike as the girl spins round just before it goes dark, then we hear the gasp as it goes black.