I agree with Tina. Try to find out what she likes, or ask her friend. Wouldn't want ring disappointment to flatten the momement. If she knows you're poking around asking her friends questions, then it might make it more fun. Or take a walk near some good jewelery window shopping and ask questions.
Besides, she has *some* idea you're going to pop the question, right? I knew Russ was going to propose (eventually

) but I didn't know when and where, so it was a surprise. Then when I figured out the day and that it was iminent, he still kept me hanging on when he was going to get it over with
PS Happy for you!!