Personally, if it were me, I would place one last call:
"Hello, so-and-so, I am giving you one last phone call to try to arrange pick up of your cookies. I made a special exception in making these for you without a deposit because you are a reputable teacher at DDs school and I never dreamed it would be so difficult to get ahold of you.
In any case, the cost of the cookies I made for you is $____. Since I have no other way to reach you, I am leaving the invoice for you with Ms. ____________ at school and would appreciate your prompt payment. As I am sure you understand, I already laid out my own money for the ingredients for your order and spent a lot of time on your custom cookies. I expect to be paid on my invioce regardless of whether you come for the cookies.
Thank you in advance for your prompt attention to this matter."
Then make an invoice, drop it off at the school and see what happens. Don't hold your breath for payment, but at least she will know that you took the high road and she can't badmouth you. Chalk it up to experience.
Sorry it happened to you.