Hey Karen. Nice to see you, though sorry to hear about the non-payment. At some point it might be better to just cut your losses. However you said this client has always paid in the past so it could be a case of them not having the money at the moment. It's wrong for them to ignore your emails, but it's happened to me before and in the end the client usually pays. It's generally taken periodic emails from me to eventually get payment.
Your other options are to start stepping up the pressure. Talk to a collections agency or similar.
This won't help you now, but in the future always ask for a deposit (50%

up front and full payment before delivering files. The deposit helps sort out those who are planning on paying from those who aren't. And people who have paid 50% are going to want to pay the other 50% to receive the files.
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