Not sure, what this means?

So there's this girl I know, she acts very strangely around me and I'm not sure what to think. She looks at me often and we catch each others eye, and sometimes she smiles but it's like a shy, apprehensive smile (she doesn't always smile). But the strange thing is she's not a shy person, she's always laughing and joking seems to be quite a bubbly person and has no trouble stating conversations or making small talk. But Everytime I approach her she seems to be a completely different person, she's a lot quieter, doesn't say anything until I speak to her, she'll just stand in silence and look at me, won't even say "hi" or anything to get my attention, her voice is normally loud and confident but around me, it's sometimes high pitched and other times it's really soft and quiet and I can barely hear her, I don't know if this is anything but she seems to stretch her words out around me etc. "See yaaaaa" or "Thankyooooou" in a quiet timid voice, I'm not really sure
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Ok thanks, we both have been exchanging eye contact for months, but sometimes when she's walking towards me she avoids my eyes like they're the sun
Not sure, what this means?
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