In the future, don't accept her request for a confirmation.
We have to operate under the assumption that she is mature and responsible enough to handle something like showing up at a place she's agreed to be without being reminded.
You can even suggest she set a reminder on her phone or computer, or have one of her girlfriends remind her.
Her asking for a confirmation can be a way to turn you down without actually saying "no" on the phone.
She agrees and asks for confirmation. Then when you contact her later to confirm (or remind in this case), that gives her an opportunity to say "something came up, I'm really sorry, let's do it again another time."
Don't accept anything less than an enthusiastic "yes" from her when you extend the date opportunity.
