Should I give my girlfriend a ring on her birthday or anniversary?

I've asked this question before and I got answers like "Propose!" We are only 15! If you're a girl, what would you think is more romantic or whatever? If you're a guy then what would you do? We have been going out for almost 9 months now. I bought her a diamond ring in December for Christmas because she wanted one. I just recently bought an opal ring that she really really wants, I bought it yesterday because it was like 80% off so I got a great price. Her brithday is in August and our 1 year anniversary is in October. What should I do? This ring isn't going to be a promise ring, I have a different style ring in mind for that. So please help, and please explain your answer. Thank you. By the way, she is planning a pretty big thing for our 1 year (I don't know what its a surprise) so I guess it would be good to give it to her then because she is going to like take me out. I also want to give it to her really soon so thats why I don't know what to do. I also don't know what to get her for her birthday if its not the ring, vice versa, I don't know what to do if for our 1 year if I give her the ring for her birthday.