As I said earlier IF you decide to open the dispute then send a new invoice WITH postage before you open the dispute so if she decides to pay with paypal to close the dipsute she will also be paying for the postage.

If she pays with paypal and the postage is included you can just post it too her.

If she pays with paypal and decides to pick up then she can open a dispute for not received and as you can not prove postage she will be refunded and still have the item.

If the listing stated pickup only then that would be different but as it sounds like you have agree to allow pick up then if she paid with paypal you are at risk of her opening a dispute.

She has stuffed you around enough.

You have agreed to something that was not in the listing.

So why wait any longer?

You have given her the chance to pickup and pay so open the dispute instead of letting her dictate terms to you.