US based Ebay seller scammed me out of $1200 Australian. Paypal no help I'm over 180 days. How do I approach US attorney to send letter of demand or sue?

I'm in Queensland, Australia. I bought a $1200 Armand Nicolet "as new" from an Ebay store. The seller is employed at a Philadelphia watch shop. The watch didn't work. I paid $160 to send back so she could have her watch store repair. 2 months ago. Watch was signed for. Never heard from her since. I have her phone# and personal address. Cheers :D