At this point you don't have a customer, you have an inquiry. Send her one more message requiring payment in full by the end of the day or you'll assume that she doesn't want the cupcakes anymore. You don't need to be nasty about it, just let her know that you won't be doing the order (since she hasn't really placed an order if she hasn't paid for it.)
Since I haven't heard from you with the payment for the cupcakes we talked about, I'm assuming that you don't need them. If you do want to place the order please get the payment to me by the end of the day so that I can reserve the time for you. If I don't receive the payment by this evening I won't be able to do the cupcakes, so please let me know if you do want them.