Should you? Is there something posted? Do you two keep a joint calendar? Did she clearly say or email something? If so, then you have a problem. Otherwise she is assuming mind-reading skills which most of us men don't have or trying to blame-shift.
"...Your lack of communication has once again caused a problem."
You say: You first notified her by email on May 27, then once more, and SHE did not respond. In turn she has not told you about any of her plans.
If you feel she's blowin' smoke then tell her sorry, but plans have been made already. Suggest you either continue plans as is or have her help pay the change fees. Otherwise if you should have known something then prepare to eat some crow (prepare "Well Done" 180 degrees - those things are full of bugs).
Nonetheless there is a communication problem, either with you not paying attention and/or she not responding and both of you need to work on it. Read each others emails. Sign up for an online calendar where both of you have access. Text. Call. Whatever. You're in a business arrangement now.
Maybe others have a better approach.
"My actions are my only true belongings. I cannot escape the consequences of my actions. My actions are the ground upon which I stand." Thich Nhat Hanh
