I canceled. I just said I'd rather do it some other night. She didn't ask why and told me that she planned on going anyway, with the child. All via email, so no anger expressed on either side.

I'm still flabbergasted that someone could be so clueless -- why didn't she just cancel? Or not agree to babysit when she had other plans?

I am not sure why I keep going back to this friend or wasting as much energy as I do on how to deal with her.