She seems interested but hesitant to give me her number...why?

So I met this girl in college through mutual friends. I've only been able to have short conversations with her and she does seem interested from what I can tell.

Like she looks at me quite a lot (compared to what I'm use to around other girls) and I can't take my eyes off her either. Recently she is around me but more often (with her friends or around mine, since she knows mine too) but would never directly approach or initiate conversation with me.

I have her on Facebook. I asked her in person if she would like me to send her some study notes and she said that would be really helpful. But I didn't ask for her email since I thought I implied that she should have given it to me.

Her email address is not on her Facebook profile.

A few days later I send her a Facebook message telling her I haven't forgot about sending them and asks if she still wants them. She says yes please in her message reply but again doesn't give me an address to send it to!

A week later, I post on her wall (so everyone can see) asking for her AOL (email) address directly and clearly, so I know where to send the notes to. She doesn't reply.

A week or so later, she bumps into me/friends and makes a big fuss about the subject she is doing and how it's so hard (it's the same subject I offered her notes for). So I mention the notes I have and ask if she wants them and again she says yes. But this time I go well..i need somewhere to send them to! So finally she writes her email address for me and thanks me really politely and friendly.

So I send the notes and she replies in the email thanking me a lot again but that's about it.

If she wanted to notes why didn't she give me her email address? Or she isn't interested at all and is just being nice/polite , hence no interest at all? I also assume if she was interested she would have asked some questions in her email but she didn't.

She seems interested but hesitant to give me her number...why?
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