I think this is what they mean when they say therapy is about the relationship. The situation is you had expectations and you felt disapointed by her actions. That could be the script for any number of human interactions. I think this is why they also say, when you forgive someone, its for YOUR sake, not theirs. Can you accept this person's imperfections?

"And forgive us our trespasses, as we forgive those who trespass against us"? - NOW I get what that means.

I guess the question is, is her disruptive schedule causing untenable disruptions in your schedule, or are you able to absorb them? Would you prefer to find a more stable t?