What does she like?
What does she do for fun?
Hobbies?
Interests?
Personal views? e.g Enivormentalist
failing that a vibrator
Come on... it's his sister!
I hope he wouldn't seeing that it is his sister
It certainly fills the first three questions.
Granted it would be very awkward but I think she will know the good intentions, and appreciate the thought and gift.
Did you notice when you quoted my post or did you read it(?)
She's 19 and has a Mac - that doesn't mean she wants computer gifts unless she's pretty geeky.
How about the body lotion for whichever scent she usually wears? The stores are full of coffrets at the moment where you get freebie extras too if your budget can stretch to that. Women occasionally treat themselves to perfume - they rarely spring for the extras so it's always nice to get them. If you've got a department store selling Origins, go look for their limited edition Ginger Glimmer body lotion - it's amazing stuff.
Or fashion jewellery (Murano glass hearts on thongs etc) perhaps.
If you get really stuck, buy her a gift card for a local department store so she can put it towards something she wants rather than having to say thanks for something she doesn't really want or need.
failing that a vibrator
or iVibrator by Apple