There is also the Sweetie Bracelet by Links of London. It is $220, so a bit more then you were looking to spend. But it is a great bracelet.
It all depends on what you want to get her. Let me know if you need any more ideas, I have plenty! Are you looking to get a bracelet, necklace or earrings? I can think of more if you need more!
I would def stick with tiffany! What about a sterling silver key there are some beautiful ones for 165, or a pendant would be nice, and she can use one of her own chains with it.
Pandora may be more personal, but at her sister's age it's all about status (unfortunately) so Tiffany's would provide that status and be more recognizable than Pandora, I would think.
I think a Tiffany key is an excellent idea. I'm 25 and (no offense to anyone) I'm not very excited about the "look" of Pandora and would much prefer something from Tiffany. Also, an item from Tiffany is a complete look, whereas the Pandora bracelet means that she will have to buy more charms if she wants to fill out the bracelet.