If she is going to pay with cash on pick up then it does not matter what is on the invoice.

I would be sending an invoice WITH postage in case you open a dispute and she pays by paypal to close the dispute and at least then she has paid the postage so you can just post it too her.

If she still gives you the runaround then open the dispute (but send an invoice with postage first in case she pays by paypal) and if she has not picked up or paid within 4 days after opening the dispute close it so you get your FVF back, she gets a strike and is blocked from being able to leave any feedback for you.