AITA for not canceling my plans when my friend assumed I would?

I (25F) have a close friend, “Lena” (26F). She’s more spontaneous and emotional, while I’m very much a planner. So a few weeks ago, I told her I had tickets to a small event I’d been looking forward to for months and had already taken time off work for. A few days later, she called me stressed because her cousin scheduled a last minute birthday dinner on the same night and said she really needed support. She then said, I figured you’d come with me instead. I was surprised and told her I was sorry she was stressed, but I already had plans and didn’t think I could cancel. She said that if she’d known I wouldn’t come with her, she wouldn’t have agreed to the dinner, and that friends should prioritize what’s important in the moment. She also said my event wasn’t that serious. I told her I didn’t think it was fair to expect me to cancel something I’d planned and paid for without asking me first. I did offer to help her beforehand and suggested we hang out another day. She said I was being rigid and that she sometimes feels like she can’t rely on me emotionally. We haven’t talked much since, and a mutual friend says she feels abandoned, though they also understand why I didn’t want to cancel. I feel bad, but I also feel like agreeing to last-minute expectations isn’t reasonable.