July 4th Fireworks

I’ve been very close to my niece her entire life. (I don’t have children of my own and I’m her second Mom) I’ve always had her back emotionally and financially. I was her support thru her parents’ divorce.
Over the 4th weekend she wanted to bring her boyfriend’s parents to meet me and watch fireworks from our home. I had other plans which I was very much looking forward to (and it’s my Birthday). I said that day wouldn’t work but any other day would be fine. She told me she was very upset I couldn’t take 5 minutes out of my day to meet them. I explained to her that I would love to meet them but I already had my Birthday plans made.
Since then she is barely speaking to me. She didn’t even acknowledge my Birthday. Even writing this almost makes me laugh at how silly this is. I switch between thoughts:
She’s mad at me and that’s okay.
I can’t believe with all I’ve done for her she would shut me out over something so small.
I don’t deserve this.
Life long relationship ebb and flow.
She’s human and I accept her humanness.
And then there’s the thought that her behavior is almost humorous. It’s like when she was little and would get mad at me because I wouldn’t let her have a cookie (She’s 25 now).
I would love a little coaching to take the sting out of it.
Thank you