It’s impossible to know without asking. I’ve had too many instances where a women being nice, smiling at me, being touchy etc meant simply that she was a nice affectionate person.
No man really knows if a woman likes him until the first kiss.
Back when I was 13, there was a lot of person A asking their best friend to ask person B’s best friend if person B liked person A or liked person A. The phrase “… likes you as a friend” was uttered a lot.
You know, if you’ve been totally best friends for like forever, you probably hang out a lot together anyway. In my day, there might be movies or bowling or listening to records involved. So you’re just thinking of adding smooches and snuggle bunnies to the relationship, right? I mean, at 13 I think you’re too young for sweaty snuggle bunnies. If you’re truly friends, if she’s not interested in that way, you’ll still be able to hang out together and you can look for romance from someone else.
Tangential anecdote. When my parents met, back in the 40’s, my father called and asked her out for a Friday, but she had plans and said so. She definitely liked him, but there was a pregnant pause until he said, “OK, how about Saturday?” She was so relieved. Me too: otherwise I’d have different parents, and I like the ones I got. 
Back to the OP. At such a young age, there are a lot of variables.
Just a few years older, and I’d say that except for a few very socially awkward women, when a woman wants your affection, you’ll find it’s easy to give it, and if she doesn’t, you’ll find it’s hard to arrange it. I have no idea whether this is instinctive or learned behavior on their part, but it’s a remarkably sound principle (unless they’re coy and playing hard to get, but hopefully you’re not at that level of gamesmanship!)
I wouldn’t be surprised if it’s the same way at 13, if she’s not socially awkward. (I don’t mean that as a put-down. Some great people are awkward, and it just takes a little more effort to figure stuff out with them.)
If she makes it easy for you to touch her (as in, hold her hand), chances are, she’s interested. If she doesn’t, chances are, she’s not. If she lets you get very close while talking, chances are she’s interested, and if not, probably not.
Chance favors the bold. If you make a bold chance and get rebuffed, you can always say something like, “Hey, you’re a hottie. I had to at least try!” and laugh. As long as you don’t moon and pester her, you won’t ruin a good friendship. Plus she’ll take the compliment, and who knows, maybe in a couple years the tables will turn.
Good luck!