I think you should tell her in person.

A therapist has a special role in your life. Her job is to ALWAYS put you first. You are not supposed to worry about hurting her. And I doubt she was hurt, she probably was very disappointed in herself, and felt terrible about how it made you feel.

Abandonment is a big deal. It's one of the most important things therapists learn about in their training. It is a failure on a therapist's part if they abandon a client. When she didn't show up, you very rightly experienced that as abandonment.

Your feelings about it are very legitimate. I think she will feel better about the whole thing if you talk to her about it when you see her next. Don't worry about her feelings. It's her job to manage her feelings, and I'm sure she will. Your job is to talk about how you experienced it, and that will give her the opportunity to repair the rupture in your relationship with her.

I hope it goes very well!