Girls, Why would a girl joke with me about something?

We both got around equipment that was ordered for our volunteering work. The girl I like I said as a joke " you should have gotten the smaller size jacket". The reason she said that was I didn't get mine cause they didn't have my size in stock. She was joking though. Then the other thing was she started laughing about something I was doing that wasn't working out. She said " sorry I shouldn't laugh" it was definitely nothing personal and I kinda laughed too.

Girls, Why would a girl joke with me about something?
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