I agree with beso.
And even though it's a terrible thing to say to people, and they normally choose to think they are the exception to the rule. But at 13, you and your girlfriend would be going through puberty, and it makes life very difficult, and you don't know which way is up. Have you met your girlfriend in person?
You cannot be in love with someone over the internet if you have never met. Maybe love... Maybe infatuation. But not love. To be in love with someone, you have to be able to see their facial reactions, be close to them, touch them, know their smell. Things that you cannot know or see over the internet.
You should tell your parents, if you want to meet her. Why would they make a big deal out of it?
I know it's difficult, I've been in the same situation. I was 16 and met someone over the internet. I thought he was lovely. We met a couple of months later and now after a long time of meeting up pretty much every weekend. We now live together and are very happy.