Why would a girl start giggling when I wave at her?

There’s this girl I like A LOT. I’ll admit maybe I make it obvious like I wave and say hi when I see her. I recently told one of my work friends I liked her and they said she’s single and that they don’t know if she likes me. Then next day I walk in and when I wave she giggles and waves back I don't know if that’s a sign or if I’m thinking too much into it but I’m starting to talk to her more and got her Instagram. But is that a sign?
Why would a girl start giggling when I wave at her?
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