Buy a Bracelet

Don't buy her a ring!! Rings are extremely powerful symbols and you can easily scare someone off by showing them a ring box! Instead, braid her a bracelet, or buy an inexpensive one at the mall. The point is not that this is an "expensive bracelet with diamonds". You're not trying to buy her love. The aim is to give her something that she can wear and think of you. If it can be handmade, it is far better, as long as it's something reasonably attractive that she could wear.