Hard to read... Options

[DisOriental85]

Here is the story:
There is the girl, M who I like... I'm not sure if she likes me back because I think and so do other people, that she is hard to read... M and I have math class at the same time, not the same class, but it was 2 doors down from one another... So we would walk to class together in the mornings and we would talk about the weather, stuff we did the night before and such... Well, one day, she was running late for class and she told me that she had a math test before, so I messaged her on Facebook asking how the test went and if she ran late to any other classes. Well, she "poked" me on facebook and told me that it went well and that she hasnt ran late... So we started a poking war, in which we kept "poking" one another, leaving each other comments like, "Im gonna win," and basically joking around with one another... About a week and a half passes by... Well, one day, on the way to my 900 class, she and I were walking in the same direction and we walked to her car, in which she gets her laptop and while we were getting the laptop, we talked. It seemed as if almost every other sentence I said to her was funny so she laughed. Well, I asked her where she would be and when she said the library, I told her that I might swing by before I go to work... That day, my class got out early, so I went to the library. She was alone in one of the study rooms so I joined her, while she was doing math and I was just on the computer. I caught her looking at me and then looking straight down and when I spoke to her, she would look at me, then look down... Time came for me to leave and go to work... BTW, she won the poking war... But we kept messaging one another and I guess during this time, I fell for her even more... I talked to her older sister, J whom I was close with, a very good friend of mine, and I asked if it was ok for me to talk to her sister M. She said that M was talking to someone but if I wanted to, go ahead, but be careful... I've gotten advice from friends saying that I should just talk and get to know her more before asking her anything about dating, and then some who are like, "no, don't try to talk to her". My best friend tells me because he has been around their families that the family won't like me dating their daughter...
The other day, she and I joked around, messing with my phones, when I took pictures of her but she deleted them because she didnt want me to take them... She and I also have this joke where I am on restrictions, and I am in time-out. I like her and I havent asked for her number yet, and I was wondering, how I should ask her without directly going, "Can I have your number?" The basic thing is, I'm pretty sure she knows that I like her, how can I tell if she likes me any at all? Any hints that I should keep an eye out for?
Thanks...
Confucious says Thanks to all!