Boundary issue?

I’m joining an online course right now. And part of it is to work with my peers. And I like that.

One of my peers has canceled our scheduled calls with me a few times. Just less than a day before they should start.

I like her, even if working with her is difficult for me. But that’s OK, so I can learn.

Now she canceled our appointment for today. She explained it and I get her reasons. Still, my thoughts about it make me angry, hurt, and misused. Like being on her mercy and not self-determined.
My thoughts go like: She doesn’t value my time. I’m just a stopgap for her. She misuses me and my time. She’s egoistic. She thinks I’m always available for her. And maybe I am.

What did I do? Once I canceled an appointment like a sullen child. I feel resentment and still try to be nice and friendly. I remember other situations with other people when I felt that way. My head is spinning. And I tell myself things like: Come on, don’t be a jerk.
And I recognize, none of this helps.

What do you think: Is this a violation of boundaries? Even if I didn’t tell her?
Or should I change my thoughts about this C?

What would be a good thing – especially to not be triggered with that kind of behavior by other people anymore?
And if it were a boundary issue, what would be a good move?

Any thoughts, tips, and hints would be helpful. Thanks!