Explain this to me

Went on a first date this weekend with someone I recently matched with. It (seemingly) went well. It was quite long. She was chatty and even paid for dinner when I wasn't looking.

We went to a 2nd place for drinks (which I paid for). Again, lots of conversation, laughter, etc.

Last 20 minutes or so. She was a different person. She got weird when it came time to say goodbye. She lived around the corner from our final pit stop. I asked her if she wanted me to walk her home. She said no. We hugged, there was an awkward kiss (just a peck), and I said I'd text her the next day to plan something.

I said good morning and sent a funny gif. She responded with a one-word answer. Conversation was like pulling teeth with her.

She went from spending the better part of a day with me and paying for my dinner, to barely speaking to me.

I just don't understand people.