She will need the email address you use as your PayPal account name, but that's all. PayPal has been holding payment until product arrives, but I haven't seen otherwise. You can simply hold the product until payment clears. Tell her that up front.
It does sound a little strange, but then some strange things do occasionally happen. If you can rectify the extra money in your mind then try the above. Otherwise, I agree that anytime someone offers you more than your asking price you should be wary.