Girls: is this a weird thing to say?

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Perhaps you should know she's stared at me several times (she doesn't seem attached to anyone, really) and we already talked once (which was very pleasant), but we don't share any classes (we go to the same Uni).
Oh, and once I saw her and I winked at her, and she waved right back at me.
Is it OK to tell her something like
"Hey, we can only talk if we run into each other. (Like being sad about it) How can I find you on Facebook?".
Or would be too weird?
See, since she doesn't seem attached to anyone (shy or introverted?) I don't want to be too pushy.
What's a better way to do that?
Thanks! (Oh, yes, I am so clueless).