Go to the invoice.
Cut the shipping price.
Do NOT hit recalculate.
Send.
Accept cash from the buyer on pickup.
Mark the transaction Paid.
Leave feedback.
BTW. If the buyer is picking up, do not accept Paypal payment. This requires proof of delivery in cases of Dispute. Cash on pickup is not only allowed by eBay, it is encouraged by your fellow sellers.
The buyer is usually protected from mail order problems by PP. When she picks up, she can inspect the item and perhaps even change her mind. And that's okay too. The seller is protected by having money in his pocket.