Hi,
If she has a static IP, you can block her IP even though she can use another one. You can block her email, but she can create another one. I would refer to your return policy and would never refund shipping costs. You're a business guy and not social welfare. Don't accept anything that has been opened. You won't be able to sell it anymore. If she returns something, I would not accept the return and let it go back.To avoid bullshit in the future, add to your policy that returns can only be made after receiving a return number from you, anything else is not accepted. If she opens a claim with Paypal, refer to your Policy where everything is clearly stated. And third but not least, you are not liable for damage during shipment. Tell her she needs to contact the shipping party to make a claim.
Cheers.