Why would a girl that shows interest, suddenly decide to give a cold shoulder?

Anonymous
So there's this girl from the highschool I'm at, and we never really hanged out or talked there at all. Never batted an eye on her (she does look nice though). Then, a few weeks ago, during semi-lockdown (cafes still working till 6pm), she suddenly starts messaging me. She sends all sorts of flirty messages, laughing at my jokes and keeping the convos going. She wants to chat past midnight up to 3 in the morning. This goes on for a week, so I ask her if she wants to go somewhere for drinks. She says sorry I can't now, and when I ask when she can, she responds "when lockdown ends". So I thought that was a simple rejection. Alright, I don't message for a few days. She starts messaging me again 4 days later. She invites me to a party a couple of her friends are having for the winter holidays. Some messages happen in the week between, but she starts being weird and taking hours before responding. There, at the party, she doesn't really talk to me or anything. Straight up acts as if I weren't there. Just a hi and later a bye. I tried talking to her but she just gave quick responses to shut the convo off. What the hell is this chicks deal? Did I do something I'm too dumb to see or is she just bonkers?
Why would a girl that shows interest, suddenly decide to give a cold shoulder?
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