Boyband, Twilight, and sports. Sounds like a teenage girl that likes sports if you ask me. My sister loved basketball, She had a room with female basketball stars (WNBA), backstreet boys posters, movie posters (Especially basketball movies). Just because there arnt unicorns and butterflies doesnt mean its a boys room. Everyone has their own personality, ND is notorious for detail, They were showing who she was by using her room.
I think what made Sarah so special was that her room wasn't filled with unicorns and sparkles. She seemed way more belivable and loveable because you could tell she was strong willed but a really sweet person. Somebody who could take care of themselves yet didnt mind having someone there for them. That definitly wasn't a "boys room" though.
As for how she got the money. Does it really matter? We saw maybe 10 minutes of her life and we the player along with Joel the father will never really know how she got the watch. But doesn't that add something special too it. Here is somebody that clearly doesn't have much of her own money but still was able to get something so nice for her father.