Why do I have these feelings?

It could very well be sisterly. I knew plenty of girls who got confused about their uality because they idolized another girl and didn't know if it was a romantic crush or friendly obsession. You have these feelings because you have crazy hormones flowing and you're a 13 year old human being. Totally normal. And theres nothing wrong with swinging both ways if you know what I mean. Just let stuff happen, you're feelings are yours and it doesn't nessescarily mean anything about you as a person if you feel a certain way.