Girls, Should the guy or girl add the other on facebook?

This girl and I have spoken heaps and we get along very well. Over the last few months there has been something between which I haven't quite put my finger on it. There has been signs she likes. But I've waited to see if she will add me on Facebook and she hasn't. Should I wait for her or just add her?
Girls, Should the guy or girl add the other on facebook?
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