It's obvious from you said that you feel that there could be a good connection/working relationship with this therapist. She made a significant error twice by not paying close attention to her schedule: 1) She should know ahead of time if she isn't able to meet with you the next Saturday because she has a previously scheduled event (co-leading a group). This is not good self-management of one's schedule, but we all make these mistakes now and then. But then, 2) She should have been aware before you even came in for your next appointment that the following Saturday was a national holiday, and she should have already made her decision about whether or not she was taking it off--again, poor management of her schedule and not a good sign that she repeats the same mistake twice in a row. Having a consistent, stable therapy frame is important and a therapist who is doing things willy nilly is not giving her clients' needs the importance they require. Sure she has to pay attention to her family's needs, but part of doing that is staying on top of your own schedule!

But that said, it could have just been a bad couple of weeks for her and working with a therapist that you feel "good about" is important, so like Rainbow mentioned in her post, it might be worthwhile to talk to her about how the two cancelations have made you feel. The other good thing about talking to her about this is that you get to see early on in the therapy relationship how she handles and owns her own mistakes. Does she get defensive when you confront her about her poor handling of her schedule? Does she own up to her fumbling things or does she just shrug off your feelings and have a "deal with it" attitude. Those are really important things to know about a therapist. Good luck!