Stood up for a play date?

It’s holiday time and scheduling play dates can prove a sanity saver. So long as the other parent doesn’t flake on you.
Our friend Carol had organized a play date with one of her daughter’s favorite preschool classmates. She thought she did everything right. She and the other mother exchanged emails a week in advance and even confirmed the night before.
At 10 a.m. — the designated drop off time — her daughter was busting with excitement to see her friend. When the little girl still had not shown up by 11:15, the excitement had given way to tears. Carol was particularly frustrated as she had passed on another play date opportunity with a good friend to coordinate this effort with her daughter’s classmate.
She called the other mother’s home and cell phones and left a polite email as well inquiring as to whether they were lost but never got a response. Meanwhile her daughter was sad and disappointed, which only made Carol more angry and unsure of how to handle the situation
She really wanted to shake the other mom by the collar and shout “Who does that? If something came up, call or email” but since the other parent is the mother of her daughter’s classmate, she worried about affecting the kids’ friendships/social status. Has this ever happened to you? How did you handle the situation?