My crush giving me mixed signals. What should I do?

[James]

Here's what's been happening so far:- (I'm 16 never had a girlfriend before)
There's this girl that I really like we're friends, we're both 16, I'm really shy and think she is to, we're both socially awkward and Gamer | Geeks.

First off, we talk loads, and I mean loads (we talk about games, TV, and music, stuff like that), when we talk we smile at each other and throughout the conversation we look into each others eyes, we don't look away, when I finish talking she'll ask me a question or tell me something interesting, when we first started talking she was always looking down, talking really quick and stuttering on some words, now it's not so much.
We both like almost all the same stuff, music, games etc. (This isn't even half of what we share in common).
I've made her laugh once or twice, and she's only laughed at me when I've made a complete and utter fool of myself. When I stumbled, she was the only one to laugh, she was giggling to herself. Even when I made a barely funny joke, she was the only one to giggle.
If I need anything, like a pen or a pencil or some help, she'll always help with anything I need.
Sometimes she'll ask for help off of me and it'll be something really simple.
If I talk to other people, she'll butt into the conversation, I don't mind her doing this.
When I asked for her number, she was pretty quick to give it to me, and said it so fast I had to half guess some numbers.
When I was talking to the girl we had, what I thought was, an awkward silence because I couldn't think of anything else to say to her. It lasted about 25-30 seconds, when she finally said something the conversation carried on.
The other day, after school mine and her friend shouts "Her name have a nice walk home with my name"
She replied with "Why wouldn't I?!"
Her tone was defensive, as if she was sticking up for me, but it was happy sounding, higher than her usual voice, she's done this a few times now.
She's also told me personal stuff about her, like what music and stuff she listens to, books she reads, what uni she wants to go to, that her parents are thinking of moving away when she finishes college things like that.
When we we talk I think her eyes dilate, but that could just be the lighting.
She was touching my leg with her foot as well, I think she knew she was, because she didn't stop, I'm probably just imagining this.
I've seen her, out the corner of my eyes, looking at me and if she sees I'm putting my glasses on, she'll put hers on to. Also when she was talking with this other person (boy), she leaned to the side of him and was looking directly at me as if she was talking to me.
She has been telling me more stuff about herself, like what she did the past couple of days and what she plans on doing and shows me pictures and stuff on her phone.
Also she sometimes asks for my help with really simple things.
She keeps saying that I should get twitter and Facebook. And on one occasion said "You should get twitter so I can stalk you." (I did get twitter and we talk on that to).

I thought it was going really well, but when I reply to her tweets on twitter, she doesn't respond to them, however yesterday and the day before she was replying to me.
Also I sent her a message on Xbox live, she replied to it and when I replied to her, she didn't send anything back.

Is she giving me mixed signals and is this normal for a girl to do if she likes me more than a friend?