I am going to go against most of everyone is saying here. I would not escalate the case. If you escalate it now, ebay will take at least 48 hours to make a decision (and probably even longer, since they are extremely overwhelmed with all the calls that are coming in due to the data breach). It is most likely, that ebay will decide in the buyer's favor and ask her to return the shoes. After that, the buyer will be given 10 days to upload the tracking into the case. All of that will put you well beyond the 30th. So, the buyer can wear the shoes for the even and send it back when she is done.
I would just ask her (politely and professionally) to return the shoes for the refund and give her two business days to ship it. It does not mean that she will comply, but it is worth a try.