It is okay to call and let her know you need an earlier appointment. We don't always think to say so when dealing with the initial disappointment from the cancelling.

It feels hurtful. You didn't say why she needed to cancel, but I don't think she did this to make you feel awful. I understand that it definitely hurts you, but I don't think that it is her intention. Feeling angry and wanting to retaliate by not seeing her... when you are hurting because you want to see her... feels right to you, but would isolate you further.

You may struggle with talking in therapy, and still feel trust and attachment feelings for her that are being affected by the cancellation.

Going to your appointment, honoring yourself by showing your commitment, and telling her how this affected you, will be helpful to you; these are often very good sessions and the connection and commitment are made stronger by them.