Why is she still acting interested, even after rejecting me?

I met this girl years ago as a freshman in high school... never talked to her that much but we were acquainted. This year we both got the same job at a new business. We grew a LOT closer throughout the year and a few months ago I realized I had a really big crush on her. There was a week my car broke down and she literally was picking me up from my house before 5am, and dropping me off after 2pm. I realized its really hard to spend that much time around somebody you're into without saying anything lol. So eventually, a couple weeks ago, when she started talking about that new Wicked movie that came out (I don't know anything about the movie, she's just a really big movie fan and was interested in this one), I decided to get it over with and ask her if she wanted to go see it with me. Not to my surprise, she said she "doesn't see me that way" and "would rather we just stay friends." Which is totally valid, and I told her there were no hard feelings, and within a couple days it wasn't even awkward. It was like it never happened. But the thing is, it did happen, so why is she acting like she wants me to have a crush on her? Before I asked her out, she asked me for advice on what color to dye her hair. The other day, she gave me an update that the hair dye I recommended arrived. Another example, I was watching a lot of football games yesterday, and we were texting, and I told her about something that happened in the game that I thought was cool. We ended up having a decently long conversation about football, and when I expressed the fact that the most recent game I watched was my favorite so far, she asked "how did it end? give me a recap." which is a completely normal thing to say tbf, except she has ZERO interest in football lol. She literally only asked because she noticed I was interested in it. So why is she being like this? Is she just the nicest girl ever? Am I overthinking it lol?

Why is she still acting interested, even after rejecting me?
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